Earth and Planetary Sciences › Geochemistry and Petrology

Mineralogy and Gemology Studies

Works Count: 37867

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This cluster of papers explores the geochemistry and petrology of various gemstones, including the use of Raman spectroscopy, identification of nanoinclusions, behavior of water molecules, and the formation processes of opals, beryl, sapphires, and jade.

Keywords

Gemstones; Geochemistry; Petrology; Raman Spectroscopy; Nanoinclusions; Water Molecules; Opals; Beryl; Sapphires; Jade

Salt Deposits Their Origin and Composition

1971-01-01

Otto Braitsch

Petrology of the Sedimentary Rocks

1988-01-01

J. T. Greensmith

Migmatites, melting and metamorphism

1984-07-01

John A. Percival

Oscillatory zoning in minerals; a common phenomenon

1996-12-01

Mark Shore , Anthony D. Fowler

Crystals characterized by oscillatory zoning show evidence for a quasi-cyclic alternation in the chemical composition of discrete growth-shells from tens of nanometers to tens of micrometers in thickness. Oscillatory zoning … Crystals characterized by oscillatory zoning show evidence for a quasi-cyclic alternation in the chemical composition of discrete growth-shells from tens of nanometers to tens of micrometers in thickness. Oscillatory zoning is most commonly observed and studied in crystals of magmatic plagioclase, but sensitive imaging techniques (e.g., Nomarski interference contrast microscopy, cathodoluminescence, back-scattered electron imaging, X-ray topographs) reveal its presence in many other minerals. Through the application of these techniques and an exhaustive review of the literature, oscillatory zoning is shown to occur in at least 75 rock-forming and accessory minerals comprising most major mineral classes: silicates (hydrous and anhydrous), sulfides, oxides, halides, carbonates, phosphates, and sulfates. Such mineral zoning is a common but often well-concealed phenomenon in magmatic rocks (particularly alkaline ones), hydrothermally altered rocks, mineralized rocks, and carbonate sequences. Mechanisms of oscillatory zoning are discussed, including the less-studied effects of adsorption and elastic stress in near-surface growth-layers. Its non-equilibrium chemistry makes oscillatory zoning a rich subject for further research.

Spectral information from minerals relevant for luminescence dating

1997-12-01

Matthias Krbetschek , Jens Götze , A. Dietrich +1 more

The nature of opal I. nomenclature and constituent phases

1971-05-01

J. B. Jones , E. R. Segnit

Abstract Natural hydrous silicas may be subdivided into three well‐defined structural groups—opal‐C (well‐ordered α‐cristobalite), opal‐CT (disordered a‐cristobalite, a‐tridymite) and opal‐A (highly disordered, near amorphous). Lussatite from the original locality is … Abstract Natural hydrous silicas may be subdivided into three well‐defined structural groups—opal‐C (well‐ordered α‐cristobalite), opal‐CT (disordered a‐cristobalite, a‐tridymite) and opal‐A (highly disordered, near amorphous). Lussatite from the original locality is identical with opal‐CT and thus appears to be a legitimate term for this class of opal. Although the prime criterion used is the nature of the X‐ray diffraction pattern, supplementary information from infra‐red absorption, dilatometer and thermal techniques supports the three‐fold classification.

Water in minerals? A peak in the infrared

1984-06-10

Roger D. Aines , George R. Rossman

The study of water in minerals with infrared spectroscopy is reviewed with emphasis on natural and synthetic quartz. Water can be recognized in minerals as fluid inclusions and as isolated … The study of water in minerals with infrared spectroscopy is reviewed with emphasis on natural and synthetic quartz. Water can be recognized in minerals as fluid inclusions and as isolated molecules and can be distinguished from hydroxide ion. The distinction between very small inclusions and aggregates of structurally bound molecules is difficult. New studies of synthetic quartz using near‐infrared spectroscopy are reported. These demonstrate that water molecules are the dominant hydrogen containing species in synthetic quartz but that this water is not in aggregates large enough to form ice when cooled.

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The infra-red spectra of layer silicates

1964-07-01

V. C. Farmer , James Russell

Optical Spectra of Transition-Metal Ions in Corundum

1962-05-15

Donald S. McClure

The polarized optical spectra of the ions Ti3+, V3+, Cr3+, Mn3+, Co3+, and Ni3+ in corundum single crystals have been studied at temperatures from 4.2° to 1200°K. A theory of … The polarized optical spectra of the ions Ti3+, V3+, Cr3+, Mn3+, Co3+, and Ni3+ in corundum single crystals have been studied at temperatures from 4.2° to 1200°K. A theory of the band strength based on the point-charge model and p-d mixing has been developed and applied to the data with results in fair agreement with experiment. The effects of temperature show that the vibrational-electronic contribution to band strength is quite small at low temperature but may be appreciable at high temperatures. The crystal-field parameters have been calculated as convergent lattice sums. The observed trigonal-field parameter has the opposite sign from that calculated by the point-charge model if the impurity ion is assumed to occupy an Al3+ ion position in the lattice, but has the same sign as calculated for an ion 0.1 Å displaced along the c3 axis toward the empty octahedral site. Details of the spectra have been interpreted as showing that the surroundings of an ion are distorted in some electronic states.

Apatite in Igneous Systems

2002-01-01

Philip M. Piccoli , P. A. Candela

Research Article| January 01, 2002 Apatite in Igneous Systems Philip M. Piccoli; Philip M. Piccoli Department of Geology, University of Maryland, College Park, Maryland 20742 Search for other works by … Research Article| January 01, 2002 Apatite in Igneous Systems Philip M. Piccoli; Philip M. Piccoli Department of Geology, University of Maryland, College Park, Maryland 20742 Search for other works by this author on: GSW Google Scholar Philip A. Candela Philip A. Candela Department of Geology, University of Maryland, College Park, Maryland 20742 Search for other works by this author on: GSW Google Scholar Reviews in Mineralogy and Geochemistry (2002) 48 (1): 255–292. https://doi.org/10.2138/rmg.2002.48.6 Article history first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Philip M. Piccoli, Philip A. Candela; Apatite in Igneous Systems. Reviews in Mineralogy and Geochemistry 2002;; 48 (1): 255–292. doi: https://doi.org/10.2138/rmg.2002.48.6 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Apatite is a minor but ubiquitous mineral in most igneous rocks. Although the modal proportion of apatite in common rocks is generally low, it can reach high concentrations in enclaves, cumulates, and other rocks of low abundance (i.e., rocks that constitute a small volume of the crust and mantle; e.g., nelsonites). The presence of apatite in most rocks is due not only to its low solubility in naturally occurring melts and aqueous solutions, but also to the limited ability of common rock-forming minerals to accept the amount of phosphorus that occurs in most rocks into their structure. In this paper,... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Diagenesis of siliceous oozes—I. Chemical controls on the rate of opal-A to opal-CT transformation—an experimental study

1977-08-01

Miriam Kastner , J. B. Keene , J.M. Gieskes

Linewidth and Temperature Shift of the <i>R</i> Lines in Ruby

1963-06-01

D. E. McCumber , M. D. Sturge

Improved experimental data have been obtained between 20° and 350°K for the widths and temperature shifts of the R lines in ruby. Above 77°K the results can be accurately described … Improved experimental data have been obtained between 20° and 350°K for the widths and temperature shifts of the R lines in ruby. Above 77°K the results can be accurately described in terms of Raman scattering of Debye-model phonons. There is no evidence for measurable contributions to the widths and shifts from direct processes involving emission or absorption of a single resonant phonon. Below 77°K the principal contributions are from crystal inhomogeneities.

Thermochemistry of the high structural state plagioclases

1980-07-01

Robert C. Newton , T.V. Charlu , O. J. Kleppa

Stimulated Optical Radiation in Ruby

1960-08-01

Theodore H. Maiman

Raman Effect of Corundum

1967-08-01

S. P. S. Porto , R. S. Krishnan

The Raman effect of corundum (sapphire) was measured with an Ar+ laser source. The seven expected Raman active phonons were found and their symmetry characters determined. Assignment of the internal … The Raman effect of corundum (sapphire) was measured with an Ar+ laser source. The seven expected Raman active phonons were found and their symmetry characters determined. Assignment of the internal and external vibrations of the crystals was made and the effect of birefringence in the Raman selection rules is discussed.

Chrome-rich garnets from the kimberlites of yakutia and their parageneses

1973-01-01

N. V. Sobolev , Yu. G. Lavrent’ev , N. P. Pokhilenko +1 more

A review of experimental studies of crystal/liquid trace element partitioning

1978-06-01

Anthony J. Irving

Garnet Zoning: An Interpretation Based on the Rayleigh Fractionation Model

1966-12-30

L. S. Hollister

Manganese zoning in almandine garnet is interpreted by the use of calculations based on the Rayleigh fractionation model. A close similarity of a measured manganese zoning profile and a calculated … Manganese zoning in almandine garnet is interpreted by the use of calculations based on the Rayleigh fractionation model. A close similarity of a measured manganese zoning profile and a calculated profile indicates that the assumptions used in the calculations are good. These assumptions are: complete removal of garnet from a homogeneous reservoir as the garnet crystallizes, and a nearly constant manganese fractionation factor between garnet and reservoir.

Steady-state kinetics and dissolution mechanisms of albite

1985-12-01

Lei Chou , Roland Wollast

The Stone-Čech Compactification

1974-01-01

Russell C. Walker

Refractive Indices of Rutile and Sphalerite

1951-06-01

J. R. DeVore

Prisms were made from single crystals of rutile and sphalerite and used in measuring the refractive indices of these materials. The measurements were made through the visible spectrum and extended … Prisms were made from single crystals of rutile and sphalerite and used in measuring the refractive indices of these materials. The measurements were made through the visible spectrum and extended to 1.5 microns in the infrared by the use of an infrared sensitive screen.The dispersion curves and the equations for the curves were determined. Values taken from the curves were found to agree moderately well with published values. The results demonstrate the high dispersion and the large birefringence of rutile. The experimental results also demonstrate the strong absorption of rutile in the violet end of the visible spectrum which accounts for the slight yellow color of rutile.

An IR absorption calibration for water in minerals

1997-12-01

Eugen Libowitzky , George R. Rossman

Other| December 01, 1997 An IR absorption calibration for water in minerals Eugen Libowitzky; Eugen Libowitzky Universitaet Wien-Geozentrum, Institut fuer Mineralogie und Kristallographie, Vienna, Austria Search for other works by … Other| December 01, 1997 An IR absorption calibration for water in minerals Eugen Libowitzky; Eugen Libowitzky Universitaet Wien-Geozentrum, Institut fuer Mineralogie und Kristallographie, Vienna, Austria Search for other works by this author on: GSW Google Scholar George R. Rossman George R. Rossman California Institute of Technology, United States Search for other works by this author on: GSW Google Scholar American Mineralogist (1997) 82 (11-12): 1111–1115. https://doi.org/10.2138/am-1997-11-1208 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Eugen Libowitzky, George R. Rossman; An IR absorption calibration for water in minerals. American Mineralogist 1997;; 82 (11-12): 1111–1115. doi: https://doi.org/10.2138/am-1997-11-1208 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Using IR absorption data from polarized measurements on single-crystal minerals with stoichiometric water contents (in the form of H2O or OH groups in the structure), a linear calibration curve (r2 ≈ 0.98) for water in minerals is established in the form: ϵi (the integrated molar absorption coefficient in units of cm–2 per mol H2O/L) = 246.6(3753 – ν) (ν = the mean wavenumber of the OH stretching band [in cm–1]). The investigated minerals include hydrogrossular, analcime, hemimorphite and its dehydrated phase, lawsonite, goethite, diaspore, manganite, mozartite, and pectolite. The influence of hydrogen bonding, leading to increased absorption values with lower OH stretching band energies, is confirmed. It is further shown that only the use of integrated absorbance values (band areas) results in a linear correlation with water content, whereas linear absorption data (peak heights) are not correlated. The calibration agrees with previously published quantitative IR data on staurolite and trace H in pyroxenes. It is also close to the frequently used trend of Paterson (1982). However, some of the previous calibrations of trace H in nominally anhydrous minerals, e.g., kyanite and pyrope, differ appreciably from the correlation derived from stoichiometrically hydrous minerals. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Coesite from the Dabie Shan eclogites, central China

1989-08-31

Aral İ. Okay , Shutong Xu , A. M. Celâl Şengör

The reaction albite = jadeite+quartz determined experimentally in the range 600–1200 ° C

1980-02-01

T. J. B. Holland

Highlights in Mineralogical Crystallography

2015-11-10

The Carbonate Minerals

2015-05-22

W. B. White

The principal concern of this book is the use of vibrational spectroscopy as a tool in identifying mineral species and in deriving information concerning the structure, composition and reactions of … The principal concern of this book is the use of vibrational spectroscopy as a tool in identifying mineral species and in deriving information concerning the structure, composition and reactions of minerals and mineral products. This does not mean that the approach is purely empirical; some theoretical understanding of the vibrational spectra of solids is essential to an assessment of the significance of the variations in the spectra that can be found within what is nominally a single mineral species, but which usually includes a range of compositions and defect structures. Theory alone, however, can give only limited support to the mineral spectroscopist, and careful studies of well-characterized families of natural and synthetic minerals have played an essential role in giving concrete structural significance to spectral features. The publication of this book represents a belief that theory and practice have now reached a state of maturitity and of mutual support which justifies a more widespread application of vibrational spectroscopy to the study of minerals and inorganic materials. The wide area of theory and practice that deserves to be covered has required a careful selection of the subject matter to be incorporated in this book. Since elementary vibrational spectroscopy is now regularly included in basic chemistry courses, and since so many books cover the theory and practice of molecular spectroscopy, it has been decided to assume the very basic level of knowledge which will be found, for example, in the elementary introduction of Cross and Jones (1969). With this assumption, it has been possible to concentrate on those aspects that are peculiar to or of particular significance for mineral spectroscopy.

Optical and Microwave-Optical Experiments in Ruby

1960-06-01

Theodore H. Maiman

Mineral chemistry of metal sulfides

1979-04-01

Frank M. Vokes

Glass structure by spectroscopy

1977-01-01

Roy Douglas

Nomenclature of the Amphiboles: Report of the Subcommittee on Amphiboles of the International Mineralogical Association Commision on New Minerals

1997-01-01

Bernard E. Leake , K. Linthout

Handbook of sol-gel science and technology: processing, characterization, and applications

2005-06-01

Handbook of sol-gel science and technology: processing, characterization, and applications , Handbook of sol-gel science and technology: processing, characterization, and applications , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی Handbook of sol-gel science and technology: processing, characterization, and applications , Handbook of sol-gel science and technology: processing, characterization, and applications , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

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Nomenclature of amphiboles Report of the Subcommittee on Amphiboles of the International Mineralogical Association Commission on New Minerals and Mineral Names

1997-06-02

Bernard E. Leake , Alan R. Woolley , C.E.S. Arps +7 more

Mineralogical Society of America

2021-02-01

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Cathodoluminescence in Geosciences

2000-01-01

Maurice Pagel , Vincent Barbin , Philippe Blanc +1 more

"The American Mineralogist"

1916-12-15

George F. Kay

though Quetelet mentions this writer in his "Histoire des sciences math6matiques et physiques chez les Belges," and Jules Dewert and Modeste Soons have recently written upon his work, he is … though Quetelet mentions this writer in his "Histoire des sciences math6matiques et physiques chez les Belges," and Jules Dewert and Modeste Soons have recently written upon his work, he is practically unknown to Eng- lish and American mathematicians.Born in 1508, dying probably about 1562, he claims to have been a professor of mathematics in Rome in 1546, and he certainly held such a chair in Ferrara in 1548.His works, eleven in num- ber, relate chiefly to the use of the sphere and the annulus, although some were purely astrological in their contents.

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2. The Composition of Zircon and Igneous and Metamorphic Petrogenesis

2003-12-31

P. W. O. Hoskin , Urs Schaltegger

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Mineral chemistry of metal sulfides

1978-01-01

David J. Vaughan , James R. Craig

An Introduction to Optical Dating

1998-07-09

M. J. AITKEN

Abstract Optical dating is a rapidly developing technique, used primarily in the dating of sediments deposited in the last 500,000 or more years. As such increasing numbers of Quaternary geologists, … Abstract Optical dating is a rapidly developing technique, used primarily in the dating of sediments deposited in the last 500,000 or more years. As such increasing numbers of Quaternary geologists, physical geographers, archaeologists, and anthropologists are now relying on the results produced. Written by one of the foremost experts on optical dating, this book aims to bring together in a coherent whole the various strands of research that are ongoing in the area. It gives beginners an introduction to the technique as well as acting as a valuable source of up to date references. The text is divided into three parts; main text, technical notes and appendices. In this way the main text is accessible by those researchers with a limited knowledge of physics, with the technical notes providing depth of understanding for those who require it. The first part of the book is concerned with basic notions and an introduction to the standard techniques, as well as several illustrative case histories. It goes on to then discuss the limitations of the technique and factors affecting reliability.

Spectroscopy, Luminescence and Radiation Centers in Minerals

1979-01-01

A. S. Marfunin

Magmatic Sulfide Deposits

2004-01-01

A. J. Naldrett

7. Industrial Minerals and Rocks

1954-12-31

Miloš Kužvart

Minerals from the Historic Mines of Butte, Montana

2025-06-24

Daniel Evanich | Rocks & Minerals

Resonance Raman Effect in Copper Carbonate Minerals Azurite and Malachite

2025-06-22

Julliana F. Alves , Linus Pauling F. Peixoto , Luiz Fernando Cappa de Oliveira | Journal of Raman Spectroscopy

ABSTRACT The structures of carbonate minerals, such as azurite and malachite, have been extensively studied, but some points are still unclear. This research uses Raman spectroscopy to analyze the vibrational … ABSTRACT The structures of carbonate minerals, such as azurite and malachite, have been extensively studied, but some points are still unclear. This research uses Raman spectroscopy to analyze the vibrational characteristics of these minerals, focusing on the stretching modes of the carbonate anion. The results show an unexpected intensification of the asymmetric stretching mode compared to the symmetric one, suggesting a possible resonance Raman effect influenced by Albrecht's second term. Azurite exhibited a de‐enhancement of some vibrational modes, indicating an unusual antiresonance effect, probably due to Cu(II) ions and d–d electronic transitions. Electronic spectra revealed distinct electronic transitions, with maxima at 538 nm for malachite and 466 nm for azurite. The arrangement of copper centers may deform the carbonate anion, impacting both off‐resonance and resonance effects. This study provides insights into the vibrational properties of these minerals and suggests the need for further investigations.

Adsorption of Eriochrome Black Ton Apatite Silicates: Steric and Energetic Interpretations via Theoretical Modelling

2025-06-22

Nabil Mabrouki , Lotfi Sellaoui , Rihab Ghorbali +3 more | Chemistry Africa

Ficha de Arrhopalites amorimi

2025-06-17

Douglas Zeppelini Filho , Roniere Andrade de Brito , Diego de Medeiros Bento +2 more | Datasets - Sistema SALVE - ICMBio

Thermochromic gemstone evaluation using temperature controlled in situ absorption spectroscopy

2025-06-17

Tsung‐Han Tsai , Daniel C. Jones , Christopher M. Breeding | Optics Express

Palygorskite from Sacalum, Yucatán in Maya Blue From the Eastern Maya Lowlands: New Evidence From Buenavista Del Cayo, Belize and La-ICP-MS Analysis

2025-06-13

Dean E. Arnold , Joseph W. Ball , Laure Dussubieux +1 more | Ancient Mesoamerica

Abstract Maya Blue is a unique hybrid pigment created by combining organic indigo with the inorganic clay mineral palygorskite. First used for architectonic decoration in the Terminal Preclassic, it became … Abstract Maya Blue is a unique hybrid pigment created by combining organic indigo with the inorganic clay mineral palygorskite. First used for architectonic decoration in the Terminal Preclassic, it became widespread in the Late Classic on figurines, murals, and elite ceramics. Unlike indigo, it is notable for its durability and resistance to degradation by acids, alkalines, organic solvents and fading. The authors analyzed 17 samples of Maya Blue on pottery from the Late-Terminal Classic periods, a.d. 680–860, from Buenavista del Cayo, Belize. Using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), it was determined that the palygorskite in these samples likely came from Sacalum, Yucatan, some 375 km away. The authors suggest several routes by which palygorskite might have been transported from Yucatán to Buenavista. The pigment or knowledge of how to produce it likely was conveyed through high-status exchanges rather than commercial trade. Maya Blue held significant cultural and religious importance. It symbolized water and rain and was associated with the god Chaahk . Maya Blue appeared initially at Buenavista on architecture and rare imported ceramics but its use gradually increased on locally produced Belize Valley wares. Use at Buenavista peaked in the early 9th century before disappearing around a.d. 860. The study demonstrates the potential of trace element analysis in identifying long-distance social interactions in ancient Mesoamerica.

Phase Transformations of Siderite in Different Atmospheres - Mössbauer Spectroscopy Study

2025-06-13

Mariola Kądziołka-Gaweł , Zdzisław Adamczyk , Marcin Wojtyniak +2 more | Archives of Foundry Engineering

The decomposition process of siderite (FeCO3) heated in an oxygen atmosphere and in a vacuum up to a temperature of 700oC, and the identification of the products of this process … The decomposition process of siderite (FeCO3) heated in an oxygen atmosphere and in a vacuum up to a temperature of 700oC, and the identification of the products of this process was studied using the 57Fe Mössbauer spectroscopy method. Two siderite samples were used for investigations. The measurements showed that one of the siderites was pure FeCO3, and the other had significant amounts of magnesium (Fe,Mg)CO3. The research results indicate that the siderite decomposition process begins at a temperature of 300oC. The main products of siderite decomposition are Fe-oxide nanoparticles. The crystallization process of these Fe-oxide begins at temperatures at which the decomposition of siderite almost ends, i.e., around 400oC for FeCO3 and 500oC for (Fe,Mg)CO3. The final products of siderite decomposition are hematite and magnetite or magnesioferrite. The magnetite formed in this process is poorly crystalline, what is confirmed by X-ray diffraction measurements and the shape of the Mössbauer spectra.

Chiral crossroads in Ho <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi/><mml:mn>3</mml:mn></mml:msub></mml:math> ScO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi/><mml:mn>6</mml:mn></mml:msub></mml:math> : A tale of frustration in maple leaf lattice

2025-06-12

NULL AUTHOR_ID | Physical review. B./Physical review. B

Ordered but Disordered: The Peculiar Crystal Structure of Greenalite

2025-06-01

Huifang Xu , Yiping Yang , Stephen Guggenheim +1 more | Elements

Greenalite is a chemically simple but structurally complex sheet silicate with a general formula of Fe2+(3−x−y−z)Fe3+xMgy☐zSi2O(3.5+x−2z)(OH)(6−x+2z). Originally characterized as a serpentine from X-ray powder diffraction data, detailed interrogation of its … Greenalite is a chemically simple but structurally complex sheet silicate with a general formula of Fe2+(3−x−y−z)Fe3+xMgy☐zSi2O(3.5+x−2z)(OH)(6−x+2z). Originally characterized as a serpentine from X-ray powder diffraction data, detailed interrogation of its structure through electron microscopy has revealed complex yet systematic disorder within tetrahedral-octahedral layers, and disorder in the stacking patterns of those layers along the crystallographic c-axis. These features arise from the misfit in lateral dimensions between oxygens coordinating relatively large Fe2+ octahedra and those forming the basal plane of Si tetrahedra, and result in a composition that deviates significantly from that of an ideal serpentine-group mineral. Continued interrogation of greenalite’s structure and chemistry will be fundamental to resolving problems related to its formation and stability in natural systems.

Permittivities of selected sulphide minerals: Temperature and frequency dependencies

2025-06-01

O. Marzoughi , J. Forster , R. M. Hutcheon +3 more | Powder Technology

Mineralogical Association of Canada

2025-06-01

| Elements

Mineralogical Society of the UK and Ireland

2025-06-01

| Elements

Greenalite: A Tiny Crystal with a Big Story

2025-06-01

Birger Rasmussen , Janet R. Muhling , Nicholas J. Tosca | Elements

After years of relative obscurity, greenalite is stepping into the limelight. Although first identified in late Paleoproterozoic iron formations over 120 years ago, its true extent has until recently remained … After years of relative obscurity, greenalite is stepping into the limelight. Although first identified in late Paleoproterozoic iron formations over 120 years ago, its true extent has until recently remained hidden due to its minute crystal size and inconspicuous optical properties. In the last decade, nanoparticulate greenalite has become a prime candidate in the deposition of iron formations. Together with experiments and modeling, greenalite is shedding new light on the composition of the early oceans, the role of biology in iron deposition, and H2 production during serpentinization. While the origin of greenalite is hotly debated, greenalite’s antiquity makes it an invaluable guide into environmental conditions on primordial Earth during the emergence and early evolution of life.

German Mineralogical Society

2025-06-01

| Elements

Mineralogical Society of America

2025-06-01

| Elements

Low‐Frequency Raman Spectra of Natural Pyrrhotites: Polarization Dependence for Its Lattice Modes

2025-05-28

Shu‐hei Urashima , Masafumi Kito , Satoru Nakajima +3 more | Journal of Raman Spectroscopy

ABSTRACT Pyrrhotite (Fe 1‐ x S; 0 < x < 0.125) is one of major iron sulfides found in sedimentary rocks. While it is sometimes considered merely a gangue for … ABSTRACT Pyrrhotite (Fe 1‐ x S; 0 < x < 0.125) is one of major iron sulfides found in sedimentary rocks. While it is sometimes considered merely a gangue for metal mining, it is geo/cosmochemically important mineral because its composition ( x ) and superstructure sensitively reflect an aqueous environment when it precipitated. Analyzing such properties presents difficulties, as pyrrhotite in natural rocks is often as small as micrometers and is embedded in silicate matrices. Micro‐Raman spectroscopy is a powerful tool for analyzing the crystal structure with high spatial resolution. While several researchers had reported distinctly different Raman spectra for pyrrhotite, we recently revealed that the Raman bands of pyrrhotite are extremely weak and what appear to be intense peaks likely originate from its (hydro) oxides. However, at the time, we barely observed only one Raman band at ~120 cm −1 so that even its fundamental properties such as its polarization dependence and relative intensity to other bands could not be obtained. In the present study, we optimized our lab‐built Raman spectrometer to probe weak Raman bands in the low‐wavenumber region (< 150 cm −1 ) to provide a reliable dataset for the Raman spectra of pyrrhotite. As a result, we succeeded in finding lattice modes at ~68 (), ~87 (), ~117 (), and ~230 cm −1 () with a sufficiently low baseline level for the first time, enabling us to also determine polarization dependence of their intensity.

Pfaffenbergite, KNa3(Al4Si12)O32, a polymorph of soidc feldspar isostructural with kokchetavite and wodegongijieite, found in crystallized melt inclusions in metamorphic garnet

2025-05-28

Ferrero Silvio , Lionel Sofia , Borriello Roberto +7 more | American Mineralogist

Abstract Pfaffenbergite, KNa3(Al4Si12)O32, is a new mineral found in nanogranitoids included in garnets from HP and UHP eclogites in the Saxo-Thuringian Zone of the Bohemian Massif (Saxony, Germany). The occurrence … Abstract Pfaffenbergite, KNa3(Al4Si12)O32, is a new mineral found in nanogranitoids included in garnets from HP and UHP eclogites in the Saxo-Thuringian Zone of the Bohemian Massif (Saxony, Germany). The occurrence of a new mineral phase was initially inferred based on its unique micro-Raman spectrum, characterized by a very strong vibrational mode at 412 cm−1, with minor Raman peaks at 105 cm−1, 832 cm−1, 130 cm−1 and 470 cm−1. Subsequently, three-dimensional electron diffraction revealed that pfaffenbergite is a hexagonal mineral, crystallizing in space group P6/mcc, isostructural with kokchetavite (KAlSi3O8) and wodegongjieite (KCa3(Al7Si9)O32). These two sheet silicates have feldspar stoichiometry and chemical composition, that is, pfaffenbergite corresponds chemically to an unmixed binary K-Na feldspar. Microstructural and experimental constraints suggest that it formed as the result of melt crystallization during cooling, after entrapment within metamorphic garnets. The precise pressure-temperature conditions of formation of pfaffenbergite are currently unknown. However, they must have been below the P-T conditions of entrapment of the inclusions, i.e., 1000–1050°C and 2.2 to 4.5 GPa in the present work, according to the values estimated for each individual case study. We interpret pfaffenbergite as a metastable phase crystallizing rapidly in a silicate melt enclosed in a small pore under non-equilibrium conditions, also based upon previous studies reporting the occurrence of other metastable phases in the same or neighboring nanogranitoids (kokchetavite, kumdykolite, dmisteinbergite among others). The increasing number of findings of metastable phases in the last years suggests that these minerals are more common than expected. We propose that it is even possible they may represent rock-forming minerals in natural rocks which experienced rapid cooling/rapid crystallization, for instance lavas and ignimbrites, along with experimental products involving silicate melts.

Analysis of thermoluminescence parameters of natural quartz: impact of thermal cleaning and irradiation doses

2025-05-27

Sahib Mammadov , M. A. Gurbanov , Rovshan Rahimli +3 more

Combined colorimetry and Spectroscopy: A novel nondestructive method for identifying orange garnet species

2025-05-27

Meilin Zhu , Ying Guo

Apatite chemistry from the XV IOA deposit, the Bafq–Saqand Metallogenic Province (BSMP), Central Iran: constrains on the genesis of IOA deposits

2025-05-26

Sakine Amraei , Majid Ghasemi Siani , Mohammad Yazdi +4 more | TURKISH JOURNAL OF EARTH SCIENCES

Advanced Machine Learning Methods for the Prediction of the Optical Parameters of Tellurite Glasses

2025-05-25

Fahimeh Ahmadi , Mohsen Hajihassani , Tryfon Sivenas +2 more

This study evaluates the predictive performance of advanced machine learning models, including DeepBoost, XGBoost, CatBoost, RF, and MLP, in estimating the Ω2, Ω4, and Ω6 parameters based on a comprehensive … This study evaluates the predictive performance of advanced machine learning models, including DeepBoost, XGBoost, CatBoost, RF, and MLP, in estimating the Ω2, Ω4, and Ω6 parameters based on a comprehensive set of input variables. Among the models, DeepBoost consistently demonstrated the best performance across the training and testing phases. For the Ω2 prediction, DeepBoost achieved an R2 of 0.974 and accuracy of 99.895% in the training phase, with corresponding values of 0.971 and 99.902% in the testing phase. In comparison, XGBoost ranked second with an R2 of 0.929 and accuracy of 99.870% during testing. For Ω4, DeepBoost achieved a training phase R2 of 0.955 and accuracy of 99.846%, while the testing phase results included an R2 of 0.945 and accuracy of 99.951%. Similar trends were observed for Ω6, where DeepBoost obtained near-perfect training phase results (R2 = 0.997, accuracy = 99.968%) and testing phase performance (R2 = 0.994, accuracy = 99.946%). These findings are further supported by violin plots and correlation analyses, underscoring DeepBoost’s superior predictive reliability and generalization capabilities. This work highlights the importance of model selection in predictive tasks and demonstrates the potential of machine learning for capturing complex relationships in data.

Gemological Characteristics and Coloration Mechanism of Vanadium-Bearing Beryl from Nigeria

2025-05-23

Yue Hong , Yu Zhang , Xinyi Shao +2 more

Vanadium-bearing beryl is a vanadium-bearing variety of green beryl (distinct from emerald) that exhibits an “electro-optical” green (blue-green) color, which has led to its commercial popularity. However, the underlying coloration … Vanadium-bearing beryl is a vanadium-bearing variety of green beryl (distinct from emerald) that exhibits an “electro-optical” green (blue-green) color, which has led to its commercial popularity. However, the underlying coloration mechanism remains unclear. The present study adopted standard gemological tests and non-destructive spectroscopic tests, such as X-ray fluorescence, UV-visible-near infrared (UV-Vis-NIR), infrared and Raman spectroscopy, to analyze the vanadium-bearing beryl from Nigeria. The results of these tests indicated the presence of Fe as the predominant chromogenic element of vanadium-bearing beryl, followed by V, at a level exceeding that of Cr. Furthermore, the samples displayed lower levels of alkali and magnesium when compared to other beryls, accompanied by lower refractive indices and specific gravities. Spectroscopic analysis indicates that the structural channels are dominated by type I H2O, with CO2, HDO, and D2O molecules also present. The inclusions observed in vanadium-bearing beryl bear a resemblance to those found in typical aquamarines, which are raindrop-shaped inclusions, and to those found in emeralds of various origins, which are irregular, jagged, gas–liquid two-phase/three-phase inclusions. The broad UV-Vis-NIR absorption bands at 427 and 610 nm are characteristic of V3+ (and a minor amount of Cr3+). Charge transfer between Fe2+ and Fe3+ may also contribute to the 610 nm band, which is superimposed on the absorption bands of V3+ and Cr3+. These factors primarily contribute to the blue-green coloration of beryl. The absorption induced by V3+ in the visible violet-blue region exhibits stronger intensity and a greater tendency towards the blue region compared to Cr3+. Consequently, the resultant vanadium-bearing beryl acquires the yellow-green hue (induced by V) overlaid with the light blue (induced by charge transfer between Fe2+-Fe3+ pairs), resulting in the so-called “electro-optical” green (blue-green) beryl.

Identification and source provenance of jadeite‐bearing jade axes from Ulucak Höyük, Western Anatolia

2025-05-22

Kaan Sayıt , Özlem Çevik , Alican Aktağ +4 more

Abstract The jades from Ulucak Höyük (İzmir, Turkey) are green‐colored in hand specimen, and combined petrographic, XRD, and whole‐rock analyses indicate that they mainly comprise jadeitic clinopyroxene, characterizing them as … Abstract The jades from Ulucak Höyük (İzmir, Turkey) are green‐colored in hand specimen, and combined petrographic, XRD, and whole‐rock analyses indicate that they mainly comprise jadeitic clinopyroxene, characterizing them as jadeite‐bearing jades. Primitive mantle (PM)‐normalized multi‐element patterns reveal two distinct chemical groups. Both groups display depletion in Th and U; however, Group 1 shows a narrower elemental range and marked positive Pb anomaly. The second group, on the other hand, displays a wide elemental range in most elements and strong negative anomalies in Zr and Hf ([Nd/Zr] PM = 1.6–4.2; [Sm/Hf] PM = 1.8–3.5). Regarding REE systematics, both groups are characterized by weak positive slopes ([La/Yb] Ch = 1.7–5.3). However, whereas Group 1 shows coherent LREE‐enriched trends, Group 2 displays flat‐ to LREE‐enriched patterns with a wide range in Eu. When the geochemical features of Ulucak jades are compared with the high‐pressure (HP) metamorphic rocks from Turkey and Greece, the similar multi‐element patterns of Syros eclogites (Greece) to Group 2 Ulucak jades make Syros a possible source area for the Ulucak artefacts. On the other hand, the geochemical resemblance of the Sifnos jadeite‐bearing gneisses to Group 1 Ulucak jades may raise the possibility of this island being another source for the Ulucak jades.

Formation Mechanism and Gemological Characteristics of “Yellow-Skinned” Nanhong Agate in Northeastern Yunnan, China: Evidence from Mineralogy and Geochemistry

2025-05-21

Qiuyun Song , Shitao Zhang , Wenzhou Pu +5 more

The “yellow-skinned” Nanhong agate represents a unique variety of Nanhong agate found in northeastern Yunnan, China, and it is highly valued for its distinctive yellow exterior and clear red–yellow interface. … The “yellow-skinned” Nanhong agate represents a unique variety of Nanhong agate found in northeastern Yunnan, China, and it is highly valued for its distinctive yellow exterior and clear red–yellow interface. Owing to the limited research on this variety, the present study provides the first comprehensive analysis. Field surveys and various laboratory techniques—including polarizing microscopy, scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectrometry, ultraviolet–visible (UV-VIS) absorption spectrometry, Raman spectroscopy, micro X-ray diffraction (µ-XRD) with Rietveld refinement, electron microprobe analysis (EPMA), and laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS)—were utilized to investigate its gemological, microtextural, spectroscopic, and geochemical characteristics. Field surveys identified the occurrence states of the “yellow-skinned” Nanhong agate. The laboratory results indicate that the agate primarily consists of α-quartz, with minor amounts of moganite, goethite, and hematite. The coloring mechanism observed in this study is consistent with the findings of previous studies: the external yellow coloration is due to goethite, while the internal red hue is attributed to hematite. Its unique pseudo-granular silica (Type III) structure provides a foundational basis for the later formation of the “yellow-skinned” agate variety, and geochemical data reveal the distribution patterns of elements. Based on geological surveys and experimental data, the formation of the “yellow-skinned” Nanhong agate in northeastern Yunnan can be divided into two stages: first, hydrothermal fluids filled the vesicles in the Permian Emeishan Basalt Formation (P2β), leading to the formation of primary Nanhong agate. Subsequently, the Type III primary agate underwent weathering, erosion, transport, and deposition in the red–brown sandy mudstone of the Lower Triassic Feixianguan Formation (T1f). The sedimentary environment in the second stage facilitated the conversion of outer hematite into goethite, resulting in the distinct “yellow-skinned” appearance with a clear red–yellow boundary. Based on the occurrence and stratigraphic relations, this study constrains the formation age of the “yellow-skinned” Nanhong agate to approximately 261.6 Ma.

The B-Zone 4611 Silver-Rich Pod—An Unusual Ag-Ge-Sb-As-Ni Assemblage Within the Irish-Type Zn-Pb Silvermines Deposit, County Tipperary, Ireland

2025-05-19

Colin J. Andrew , John H. Ashton

The Silvermines Pb-Zn-Ag-Ba orebodies comprise vein, replacement, cross-cutting and stratiform mineralization mostly hosted in Lower Carboniferous limestones in the vicinity of a major ENE and E-W trending normal fault array … The Silvermines Pb-Zn-Ag-Ba orebodies comprise vein, replacement, cross-cutting and stratiform mineralization mostly hosted in Lower Carboniferous limestones in the vicinity of a major ENE and E-W trending normal fault array and represent a classic example of Irish-Type Zn-Pb mineralization. Historically the deposits have been exploited at various times, but the major limestone-hosted Zn-Pb-Ba mineralization was not discovered until the 1960s. Structurally controlled crosscutting vein and breccia mineralization represent pathways of hydrothermal fluids escaping from the Silvermines fault at depth that exhaled and replaced shallowly buried Waulsortian limestones creating the larger stratiform orebodies such as the Upper G and B-Zones. The B-Zone, comprising a pre-mining resource of 4.64 Mt of 4.53% Zn, 3.58% Pb, 30 g/t Ag has a locally highly variable host mineralogy dominated by pyrite, barite, siderite, within dolomitic and limestone breccias with local silica-haematite alteration. A small, highly unusual pod of very high-grade Ag-rich mineralization in the B-Zone, the 4611 Pod, discovered in 1978, has not been previously documented. Unpublished records, field notes, and mineralogical and chemical data from consultant reports have been assimilated to document this interesting and unusual occurrence. The pod, representing an irregular lens of mineralization ca 2 m thick and representing 500 t, occurs within the B-Zone orebody and comprises high grade Zn and Pb sulfides with significant patches of proustite-pyrargyrite (ruby silvers) and a host of associated Pb, Ag, Sb, As, Cu, Ge sulfide minerals, including significant argyrodite. Although evidence of any distinct feeder below the pod is lacking, the nature of the pod, its unusual mineralogy and its paragenesis suggests that it represents a small, possibly late source of exotic hydrothermal fluid where it entered the B-Zone stratiform mineralizing system.

Composition characteristics and formation conditions of a large copper nugget from the Taymet deposit (Gornaya Shoria, Russia)

2025-05-19

Felix P. Lesnov , V. N. Korolyuk , Alexey S. Vishnevskiy +1 more

The paper contains the study results of a large copper nugget from the Taymet deposit (Gornaya Shoria, Russia). The deposit is situated in Southern Siberia in a poorly bare terrain … The paper contains the study results of a large copper nugget from the Taymet deposit (Gornaya Shoria, Russia). The deposit is situated in Southern Siberia in a poorly bare terrain and is located among basalts, trachybasalts and pyroclastic deposits of the Lower Cambrian Ust-Anzas Formation, in which porous and fragmented areas are widespread. The nugget is kept in the Central Siberian Geological Museum (Institute of Geology and Mineralogy SB RAS, Novosibirsk, museum № I-2/30). With the weight of about 700 kg, its maximum dimensions are 0.25×0.65×1.4 m. The composition of two fragments of the nugget was studied using the JEOL JXA-8230 electron probe microanalyzer with wave spectrometers, TESCAN Mira 3 scanning electron microscope with Oxford X-Max 50 energy dispersive spectrometer and the Horiba Lb HR800 Raman spectrometer. By the obtained results, copper is evenly distributed with its average content of more than 99 wt. %. The impurity elements are Si, Fe, Mn, S, Hg, Sr, Ga and Ag. Among them, silver content has the maximum value of about 0.050 wt. %. The samples are revealed for different-size (5–200 µm, seldom up to 1 mm) microinclusions of euhedral crystals of quartz and datolite, xenomorphic segregations of calcite and potassium feldspar, as well as submicroscopic grains of mercuric silver. There are small cavities partially or completely filled with quartz and calcite, along with their subordinate cuprite, chrysocolla and malachite. The transfer of copper is assumed to be carried out during the infiltration of reduced hydrothermal solutions, which are very poor in sulfur, in the composition of complexes with ligands predominantly of hydrocarbons and carbon dioxide, followed by their decomposition and the formation of a copper nugget.

The 3309 cm–1 Series in Sapphire and Ruby: A Focus on FTIR Peak Position Variation

2025-05-17

Wasura Soonthorntantikul , Aaron C. Palke

Cr-spinel seams formed by mush assimilation in the Great Eucrite, Ardnamurchan, Scotland

2025-05-16

James M.D. Day

Some of the most enigmatic petrological features of layered mafic intrusions are Cr-spinel seams. Here a new Cr-spinel seam occurrence is described from the Great Eucrite layered gabbro of the … Some of the most enigmatic petrological features of layered mafic intrusions are Cr-spinel seams. Here a new Cr-spinel seam occurrence is described from the Great Eucrite layered gabbro of the Paleogene Ardnamurchan Igneous Complex, Scotland. Laterally impersistent mm-thick Cr-spinel seams occur within cumulate anorthosite (>90 modal%, An 79-87 ) blocks that are preserved within a gravity-slumped olivine-rich gabbro raft of the Great Eucrite. The Cr-spinel grains are coarser (>1 mm) in the seam centre, with higher Al and Cr and lower Fe 3+ than smaller peripheral grains. Cr-spinel grains can be partially or wholly enclosed by thin (<20 µm) rims of olivine within intercumulus augite. The observations support Cr-spinel seam formation in situ through reaction of percolating basaltic melt within a pre-existing plagioclase and olivine dominated mush. Melt interaction led to modification of cumulus plagioclase and crystallization of Cr-spinel and intercumulus clinopyroxene. The blocks of anorthosite and Cr-spinel were preserved through incorporation into an olivine-rich gabbro slurry that gravitationally slumped on the paleo-magma chamber floor of the Great Eucrite layered intrusion. The Great Eucrite Cr-spinel seams share similarities with some Rum Eastern Layered Intrusion Cr-spinel seam occurrences and highlight the array of mechanisms for generating Cr-spinel seams in layered mafic intrusions, including those with basaltic parental melts.

Approaching the Neolithization Processes in North-Western Iran

2025-05-15

Andrea Cesaretti , Roberto Dan

Abstract One of the most investigated aspects of prehistory in the Ancient Near East is undoubtedly the Neolithic period. The scientific community has often drawn attention to attempts to reconstruct … Abstract One of the most investigated aspects of prehistory in the Ancient Near East is undoubtedly the Neolithic period. The scientific community has often drawn attention to attempts to reconstruct the complex processes of Neolithization undergone by hunter-gatherer communities. Over the last few years, much has been done to reconstruct Neolithization processes on the Iranian plateau with particular attention to the Zagros Mountain region, probably rightly considered one of the points from which Neolithic cultures spread in the upper Mesopotamia area. This contribution aims to provide a comprehensive reassessment of the available data, with discussion of several crucial aspects of the Neolithic phases of north-western Iran. These critical issues are mostly connected to the absence of systematic investigations of Neolithic sites, and to a series of problems regarding the interpretation of the scarce information available. The paper therefore provides an overview of the current state of knowledge and proposals, together with and some new suggestions concerning these issues.

Raman Spectroscopy of Amphibole Inclusions in Emeralds

2025-05-14

Stéfanos Karampelas , Ugo Hennebois , Aurélien Delaunay

ABSTRACT Emeralds frequently contain inclusions, and their study can provide valuable clues on their geological origin. For the present study, 11 emeralds containing elongated amphibole inclusions from four geographic origins … ABSTRACT Emeralds frequently contain inclusions, and their study can provide valuable clues on their geological origin. For the present study, 11 emeralds containing elongated amphibole inclusions from four geographic origins (three from Austria, one from Russia, two from Zambia and five from Zimbabwe) were investigated with an optical microscope and Raman spectroscopy. The inclusions have various sizes and shapes; curved inclusions are frequently observed in emeralds from Zimbabwe and in one sample from Zambia. Most inclusions are of actinolite; tremolite is observed in Austrian samples and cummingtonite in samples from Zimbabwe. These subtle differences in amphibole inclusions in emeralds could help identify emeralds from these mining regions.

Sourcing carnelian beads from the ancient Mesopotamian site of Kish, Iraq, 2450–2200 BCE: Stylistic, technological and geochemical approaches

2025-05-10

Jonathan Mark Kenoyer , Randall W. Law , Laure Dussubieux

Abstract Trade between Mesopotamia and the Indus Civilization is studied through the analysis of Early Dynastic III Period (2600–2350 BCE) carnelian beads from the site of Kish, Iraq. Morphological and … Abstract Trade between Mesopotamia and the Indus Civilization is studied through the analysis of Early Dynastic III Period (2600–2350 BCE) carnelian beads from the site of Kish, Iraq. Morphological and technological features of the beads are compared with beads from the Indus region. The chemical composition of the carnelian is assessed using laser ablation‐inductively coupled plasma‐mass spectrometry and compared with an extensive database of potential geological sources. These studies indicate that while all the Kish beads were fashioned from carnelian of Indian origin, some were made in the Indus region, while others were likely made in Mesopotamia by Indus‐trained craftspeople.

Direct evidence for processing Isatis tinctoria L., a non-nutritional plant, 32–34,000 years ago

2025-05-09

Laura Longo , Mauro Veronese , Clarissa Cagnato +7 more

Recovering evidence for the intentional use of plants in the Palaeolithic is challenging due to their perishable nature as, unlike chipped stone or bone artefacts, plant remains are rarely preserved. … Recovering evidence for the intentional use of plants in the Palaeolithic is challenging due to their perishable nature as, unlike chipped stone or bone artefacts, plant remains are rarely preserved. This has created a paradigm for the Palaeolithic in which plants seldom feature, resulting in a partial and skewed perspective; in fact, plants were as essential to human life then as they are today. Here, we combine morphological and spectroscopic analyses (µ-Raman, µ-FTIR) to provide robust multiscale physical and biomolecular evidence for the deliberate pounding and grinding of Isatis tinctoria L. leaves 34–32,000 years ago. The leaf epidermis fragments were found entrapped in the topography of the used surface of unmodified pebbles, in association with use-wear traces. Although their bitter taste renders them essentially inedible, the leaves have well-recognised medicinal properties and contain indigotin precursors, the chromophore responsible for the blue colour of woad, a plant-based dye that is insoluble in water. We used a stringent approach to contamination control and biomolecular analysis to provide evidence for a new perspective on human behaviour, and the applied technical and ecological knowledge that is likely to have prevailed in the Upper Palaeolithic. Whether this plant was used as a colourant, as medicine, or indeed for both remains unknown, but offers a new perspective on the fascinating possibilities of non-edible plant use.

Critical assessment of opal mining techniques, tools, market system, environmental impact challenges, and prospects — A systematic review

2025-05-09

Anteneh Yayeh Adamu , Demessie Mulu Eneyew , Assamen Ayalew Ejigu +4 more

Unravelling neomorphism: recrystallization pathways in Proterozoic microfossiliferous chert

2025-05-06

Kaitlyn Gauvey , Linda C. Kah

Early diagenetic chert serves as a critical archive of life on Earth, yet the mechanisms of chert formation and diagenesis remain uncertain. The present research deciphers chert formation and recrystallization … Early diagenetic chert serves as a critical archive of life on Earth, yet the mechanisms of chert formation and diagenesis remain uncertain. The present research deciphers chert formation and recrystallization through petrographic observations of Proterozoic microfossiliferous chert and explores its relationship to microfossil preservation. Petrographic analyses reveal that the primary chert fabric consists of a network of spherules that consist of chalcedony fibers that radiate outward from a central nucleation point. Original spherules then undergo neomorphic recrystallization that results in systematic grain coarsening and a range of distinctive textures. Subsequent recrystallization can largely erase evidence of primary spherules, but often maintains distinct internal domains within crystals that exhibit sweeping extinction consistent with initial spherulitic growth. We attribute the range of neomorphic features described here to a combination of 1) growth of initial chalcedony spherules within a silica gel that permeates the primary substrate, 2) the degree of alignment of the chalcedony fibers within and between adjacent spherules, 3) the behavior of the amorphous silica component within and external to chalcedony spherules during early neomorphic recrystallization, and 4) coalescence of adjacent grains with similar lattice orientation. Notably, in nearly all cases, remarkable fidelity is maintained in the preservation of microfossil morphology and primary sedimentary fabrics. These observations lead us to a refined model for microfossil silicification and emphasizes both the complex role of neomorphism in chert formation and the low levels of water-rock interaction required for the neomorphic process.