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Pyrope
Pyrope
Pyrope
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Pyrope
General
CategoryNesosilicate
FormulaMg3Al2(SiO4)3
IMA symbolPrp[1]
Strunz classification9.AD.25
Crystal systemCubic
Crystal classHexoctahedral (m3m)
H–M symbol: (4/m 3 2/m)
Space groupIa3d
Identification
ColorBlood red to black red, red, orange red, pink, some varieties are very dark, almost black, while others can take tones of purple to purple red, Some chromium-rich pyropes are thermochromic, becoming green when heated.[2]
Crystal habitEuhedra typically display rhombic dodecahedral form, but trapezohedra are not uncommon, and hexoctahedra are seen in some rare samples. Massive and granular forms also occur.
CleavageNone
FractureConchoidal
Mohs scale hardness7.0–7.5
Lustergreasy to vitreous[3]
StreakWhite
Specific gravity3.78+0.09
−0.16 [3]
Polish lustervitreous[3]
Optical propertiesSingle refractive, often anomalous double refractive[3]
Refractive index1.74 normal, but ranges from 1.714 to over 1.742[3]
BirefringenceIsotropic, appears black in cross-polarized light
Pleochroismnone
Ultraviolet fluorescenceinert
Absorption spectrabroad band at 564 nm with cutoff at 440 to 445 nm. Fine gem quality pyropes may show chromium lines in the red end of the spectrum
SolubilityInsoluble in water, weakly soluble in HF
Mineral associationOlivine, pyroxene, hornblende, biotite, diamond
References[4]
Pyrope garnet in eclogite - Shibino, Ural Mountains, Russia.

The mineral pyrope is a member of the garnet group. Pyrope is the only member of the garnet family to always display red colouration in natural samples, and it is from this characteristic that it gets its name: from the Greek words for fire and eye. Despite being less common than most garnets, it is a widely used gemstone with numerous alternative names, some of which are misnomers. Chrome pyrope, and Bohemian garnet are two alternative names, the usage of the latter being discouraged by the Gemological Institute of America.[3] Misnomers include Colorado ruby, Arizona ruby, California ruby, Rocky Mountain ruby, Elie Ruby, Bohemian carbuncle, and Cape ruby.

Composition

[edit]

The composition of pure pyrope is Mg3Al2(SiO4)3, although typically other elements are present in at least minor proportions—these other elements include Ca, Cr, Fe and Mn. Pyrope forms a solid solution series with almandine and spessartine, which are collectively known as the pyralspite garnets (pyrope, almandine, spessartine). Iron and manganese substitute for the magnesium in the pyrope structure. The resultant, mixed composition garnets are defined according to their pyrope-almandine ratio. The semi-precious stone rhodolite is a garnet of ~70% pyrope composition.

Distribution

[edit]

The origin of most pyrope is in ultramafic rocks, typically peridotite from the Earth's mantle: these mantle-derived peridotites can be attributed both to igneous and metamorphic processes. Pyrope also occurs in ultrahigh-pressure (UHP) metamorphic rocks, as in the Dora-Maira massif in the western Alps. In that massif, nearly pure pyrope occurs in crystals to almost 12 cm (5 in) in diameter; some of that pyrope has inclusions of coesite, and some has inclusions of enstatite and sapphirine.

Pyrope is common in peridotite xenoliths from kimberlite pipes, some of which are diamond-bearing. Pyrope found in association with diamond commonly has a Cr2O3 content of 3–8%, which imparts a distinctive violet to deep purple coloration (often with a greenish tinge) and because of this is often used as a kimberlite indicator mineral in areas where erosive activity makes pinpointing the origin of the pipe difficult. These varieties are known as chrome-pyrope, or G9/G10 garnets.

Mineral identification

[edit]
Pyrope aggregate.

In hand specimens, pyrope is very tricky to distinguish from almandine; however, it is likely to display fewer flaws and inclusions. Other distinguishing criteria are listed in the adjacent table. Care should be taken when using these properties as many of those listed have been determined from synthetically grown, pure-composition pyrope. Others, such as pyrope's high specific gravity, may be of little use when studying a small crystal embedded in a matrix of other silicate minerals. In these cases, mineral association with other mafic and ultramafic minerals may be the best indication that the garnet you are studying is pyrope.

In petrographic thin section, the most distinguishing features of pyrope are those shared with the other common garnets: high relief and isotropy. Garnets tend to be less strongly coloured than other silicate minerals in thin section, although pyrope may show a pale pinkish purple hue in plane-polarized light. The lack of cleavage, commonly euhedral crystal morphology, and mineral associations should also be used in identification of pyrope under the microscope.

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Pyrope

View on Grokipedia
from Grokipedia
Pyrope is a calcium-free belonging to the group, distinguished by its vibrant deep red color and Mg₃Al₂(SiO₄)₃, where magnesium occupies the dodecahedral sites and aluminum the octahedral sites in its isometric . Named from the Greek words for "" and "eye" due to its fiery red hue, pyrope forms under high-pressure and high-temperature conditions, primarily in ultramafic igneous rocks such as and eclogite, as well as in pipes associated with deposits. With a Mohs of 7 to 7.5, vitreous luster, and ranging from 1.71 to 1.75, it is prized as a durable , often exhibiting transparency from transparent to translucent and a , though pure end-member pyrope is rare and typically colorless without impurities such as iron and that impart its characteristic blood-red to purplish-red tones. As a key member of the series, pyrope commonly forms intermediate compositions with (iron-rich) or (manganese-rich), resulting in varieties such as —a purplish-red almandine-pyrope mix—or chrome pyrope, which displays ruby-like color from inclusions and is sourced from localities like Arizona's anthill garnets or . Its specific gravity of approximately 3.58 to 4.3 and lack of cleavage make it suitable for into jewelry, where it serves as a and is valued for its lively dispersion, though stones larger than 1-2 carats often appear overly dark due to absorption. Notable occurrences include metamorphic terrains in the (the type locality for Bohemian garnets), (famous for "Cape rubies"), , , and the (Arizona and ), with pyrope also serving as an indicator mineral for exploration in kimberlites. Historically, pyrope has been utilized in jewelry since ancient times, with the 19th-century Bohemian garnet industry in the producing intricate pieces that supported local economies, and exceptional specimens housed in museums like those in and . In modern , its value is determined by factors such as color intensity, clarity (often marred by inclusions like ), cut quality, and carat weight, with high-quality chrome pyrope commanding premium prices among collectors and jewelers. Beyond adornment, pyrope's stability under mantle conditions provides insights into Earth's deep geology, aiding petrological studies of ultramafic rocks and zones.

Etymology and History

Name Origin

The name pyrope derives from the term pyrōpós (πυρώπους), meaning "-eyed" or "fiery," a reference to the gemstone's intense hue that evokes the glow of . This etymology highlights the stone's distinctive color, often likened to glowing embers or the vibrant seeds of a , which has long captivated observers for its luminous quality. Early descriptions of pyrope appear in classical texts as a prized red gem. The Greek philosopher Theophrastus, in his treatise On Stones around 300 BCE, alluded to similar fiery red gems termed anthrax, sourced from regions like India, though the identification with modern pyrope remains tentative due to overlapping ancient nomenclature for red minerals. More explicitly, the Roman author Pliny the Elder documented the carbunculus—encompassing pyrope among other red gems—in his Natural History (c. 77 CE), noting exceptional specimens from India and the Hercynian Mountains (present-day Bohemia in the Czech Republic), where he praised their brilliance as surpassing that of fire itself. The formal mineralogical recognition of pyrope as a distinct within the group occurred in the early . In 1803, German geologist classified it based on improved chemical analyses that differentiated it from related garnets like , retaining the ancient name to emphasize its characteristic fiery red coloration. This classification solidified pyrope's place in systematic , distinguishing it by its magnesium-aluminum composition.

Historical Uses

Pyrope, a vibrant red variety of , has been prized for its deep crimson hue since antiquity, often symbolizing , , and in cultural artifacts. In , pharaohs incorporated pyrope garnets into necklaces, beads, and inlays for ceremonial and funerary purposes, with examples entombed alongside rulers to safeguard them in the . The gem's intense red color evoked life force and vitality, making it a favored material for amulets believed to ward off evil. In , pyrope garnets appeared in signet rings used to seal documents, as well as in jewelry and soldier's talismans, where the stone's fiery appearance was thought to inspire and repel wounds in battle. These early applications highlight pyrope's role as both a decorative and symbolic element across Mediterranean civilizations. During the Middle Ages, pyrope garnets gained favor among European nobility and clergy, often set into rosaries and religious ornaments to denote piety and status. The gem's blood-like red was associated with Christ's sacrifice, leading to its inclusion in ecclesiastical jewelry and noble adornments across courts from England to the Holy Roman Empire. As the traditional birthstone for January, pyrope also carried personal significance, symbolizing fidelity and friendship in betrothal gifts among the elite. This period solidified pyrope's prestige, with larger, translucent specimens reserved for high-ranking individuals, underscoring its transition from utilitarian beads to symbols of divine favor and social hierarchy. The 18th and 19th centuries marked pyrope's zenith through Bohemian garnet jewelry, sourced primarily from deposits in what is now the , then part of . Artisans in centers like Turnov and Jablonec polished small pyrope crystals into intricate rose-cut pieces, creating elaborate parures, brooches, and earrings that blended affordability with elegance. These s, exported widely to and America, became a staple in middle-class and noble wardrobes, with production peaking during the when demand for colorful, versatile gems surged. Bohemian pyrope's popularity stemmed from its vivid color and workability, fueling a cottage industry that supplied rosaries, mourning jewelry, and fashion accessories, often foiled to enhance brilliance. By the late , pyrope's prominence waned as synthetic alternatives like and early lab-created rubies offered cheaper imitations, diminishing demand for natural stones amid shifting tastes toward lighter gems. Bohemian deposits, once prolific, faced depletion, further curtailing supply. However, in the and beyond, pyrope experienced a revival through markets, where Victorian and Bohemian pieces are sought for their historical craftsmanship and authentic color, attracting collectors and reviving interest in the gem's cultural legacy.

Composition and Structure

Chemical Composition

Pyrope is the magnesium aluminum end-member of the group, with the ideal Mg3Al2(SiO4)3\mathrm{Mg_3Al_2(SiO_4)_3}. This composition consists of three magnesium cations occupying dodecahedral sites, two aluminum cations in octahedral sites, and three tetrahedra forming the framework structure characteristic of garnets. As part of the pyralspite subgroup, pyrope forms a complete series with (Fe3Al2(SiO4)3\mathrm{Fe_3Al_2(SiO_4)_3}), where iron substitutes for magnesium, and with (Mn3Al2(SiO4)3\mathrm{Mn_3Al_2(SiO_4)_3}), leading to compositional variations in natural specimens. Pure end-member pyrope is exceedingly rare in nature, with most samples exhibiting impure varieties due to these substitutions. Trace elements such as (Cr³⁺) and iron (Fe²⁺/Fe³⁺) commonly substitute into the pyrope lattice, influencing its color intensity; for instance, small amounts of impart the deep red hue typical of Bohemian pyrope, while can contribute to pinkish tones in certain varieties.

Crystal Structure

Pyrope belongs to the group and crystallizes in the isometric () crystal system, characterized by high symmetry and the Ia3d (No. 230). This defines the atomic arrangement where the structure consists of a framework of corner-sharing polyhedra, including isolated silicate tetrahedra [SiO₄] at the Z sites, octahedral [AlO₆] units at the Y sites, and irregular dodecahedral [MgO₈] coordination at the X sites. The general garnet formula A₃B₂(SiO₄)₃ is realized in pyrope with Mg occupying the A (dodecahedral) sites and Al the B (octahedral) sites, forming a rigid three-dimensional network that contributes to the mineral's stability under high-pressure conditions. The unit cell of pyrope is cubic with a lattice parameter a ≈ 11.459 Å and a volume of approximately 1504.67 ų, containing Z = 8 formula units. This parameter reflects the end-member composition Mg₃Al₂(SiO₄)₃, with slight variations possible due to minor substitutions, though the cubic symmetry is generally preserved. The silicate tetrahedra are regular, with Si-O bond lengths around 1.65 Å, while the octahedral Al sites feature Al-O bonds of about 1.90 Å, and the dodecahedral Mg sites show Mg-O distances averaging 2.30 Å, all interconnected without sharing edges or faces beyond corners. Pyrope crystals typically exhibit dodecahedral () or trapezohedral habits, often subhedral to euhedral, though they may appear granular or massive in aggregates. In mantle-derived samples, such as xenoliths from kimberlites, crystal sizes range from microscopic grains to several centimeters, reflecting growth conditions in and eclogite assemblages. These habits arise from the cubic , with faces corresponding to {110} for dodecahedra and {112} for trapezohedra, influencing the mineral's external morphology in geological settings.

Physical and Optical Properties

Mechanical Properties

Pyrope possesses a Mohs hardness of 7 to 7.5, which provides sufficient for jewelry applications while remaining susceptible to scratching from harder substances like or . The specific of pyrope typically ranges from 3.62 to 3.87, reflecting its relatively low compared to iron-rich garnets such as (specific gravity 4.00–4.30), attributable to the dominance of magnesium over heavier iron in its composition. Like other garnets, pyrope exhibits no cleavage and displays a conchoidal to uneven , contributing to its brittle tenacity during cutting and polishing.

Optical Characteristics

Pyrope garnets are renowned for their vibrant hues, which are central to their appeal as gemstones. In its pure form, pyrope (Mg₃Al₂(SiO₄)₃) would be colorless, but natural specimens invariably display coloration due to trace substitutions of Fe²⁺ for Mg²⁺ and Cr³⁺ for Al³⁺, which introduce absorption bands in the that transmit light while absorbing complementary wavelengths. These colors range from deep crimson and blood- to wine- and purplish- tones, with the intensity often enhanced by the relative proportions of these chromophores; for instance, higher Cr³⁺ content can impart a more vivid, fiery reminiscent of the gem's name, derived from "pyr" meaning . This distinctive not only defines pyrope's identity among garnets but also contributes significantly to its value in jewelry, where eye-clean stones with strong, saturated color command premium prices. The mineral's interaction with further underscores its gemological desirability through high transparency and brilliance. Pyrope is typically transparent to translucent, allowing excellent transmission that accentuates its color depth in faceted cuts. Its isotropic results in a single value of approximately 1.74, producing consistent sparkle without doubling of facets, which is ideal for gem cutting. Lacking , pyrope shows no color variation with orientation, ensuring uniform appearance from all angles—a trait that simplifies identification and enhances its suitability for symmetric jewelry designs. The luster ranges from vitreous (glass-like) to subadamantine (diamond-like), contributing to a bright, reflective surface that amplifies the stone's fiery glow under illumination.

Occurrence and Formation

Geological Settings

Pyrope, the magnesium-rich end-member of the group, primarily forms in ultramafic rocks within the under high-pressure and high-temperature conditions. It is a key constituent of , particularly and , where it stabilizes at depths of approximately 50–150 km, corresponding to pressures of 1.5–5 GPa and temperatures of 900–1300°C. In these environments, pyrope coexists with , orthopyroxene, and clinopyroxene, reflecting the magnesium-aluminum composition that enables its stability in the lithospheric . Pyrope also occurs prominently in eclogite, a dense derived from basaltic protoliths subducted into . Eclogitic pyrope forms at similar depths, often exceeding 60 km, in assemblages with omphacite and sometimes or , under pressures greater than 2 GPa and temperatures around 600–800°C. These conditions are typical of zones, where pyrope's incorporation of minor calcium components distinguishes it from peridotitic varieties. Pyrope is frequently associated with diamond-bearing kimberlites and lamproites, where it appears as xenocrysts or within mantle-derived xenoliths transported rapidly to the surface during volcanic eruptions. Chromium-rich pyrope (G10 type) in these settings indicates origins from the diamond stability field at depths of 150–200 km, serving as a geochemical indicator for prospective deposits. Lamproites similarly host pyrope xenocrysts, linking it to volatile-rich, ultrapotassic that samples the subcontinental . Secondarily, pyrope forms in metamorphic terrains through regional of magnesium-rich sediments, such as dolomitic or siliceous carbonates, under high-grade conditions like or . These occurrences arise in zones, where pressures of 0.5–2 GPa and temperatures of 600–800°C transform protoliths into pyrope-bearing schists or gneisses, often with or . This process contrasts with primary mantle formation by involving crustal rather than deep lithospheric sources.

Principal Localities

Pyrope, a magnesium-aluminum garnet, is sourced primarily from mantle-derived rocks such as peridotites and kimberlites, with key deposits concentrated in several global regions. The , particularly the region, stands out as a historic and ongoing source of gem-quality pyrope. Alluvial deposits near Podsedice and Linhorka Hill yield small, vibrant red crystals suitable for jewelry, with daily production around 2.6 kg of concentrate containing 74-75% pyrope and 1.5-2.5% Cr₂O₃. These Bohemian pyropes have been mined since at least the , fueling a major gem-cutting industry. In , pyrope occurs abundantly in pipes around Kimberley, where it forms part of the "Cape ruby" suite with pyrope contents ranging from 56-86 mol%. These deposits, associated with diamond-bearing rocks, provide large quantities of chrome-rich pyrope as xenoliths. In the United States, significant sources are found in exposures of and , notably at Garnet Ridge in , and Buell Park in New Mexico, where ants excavate bright red pyrope nodules up to 1.3 cm, known as "ant-hill garnets." Other notable localities include historical samples from , where pyrope has been reported in regions like and since ancient times, often in alluvial contexts. In , pyrope appears in eclogites of , though in limited quantities as part of mantle-derived assemblages. Russia's Yakutia region, particularly the Sakha Republic's fields like the and Udachnaya mines, yields chrome-rich pyrope as diamond exploration indicators from over 1,000 pipes. Madagascar is a significant source of gem-quality pyrope, primarily from alluvial deposits in the southern and central regions, producing transparent to translucent red crystals used in jewelry. also hosts pyrope in metamorphic terrains and alluvial gravels around the area, where chrome-bearing varieties occur alongside other garnets. Production of pyrope reached a historical peak in 19th-century , driven by Bohemian mines that supplied opulent jewelry across the continent. Today, supply shifts toward modern alluvial operations in the and mantle xenoliths from sources in and , supporting both gem and industrial uses.

Gem Varieties

Pyrope, renowned for its deep red hues, encompasses several gem varieties distinguished primarily by color variations and influences. The represents a classic subtype, characterized by its intense, blood-red coloration derived from impurities (Cr₂O₃ content of 1.5-3%) in the magnesium-aluminum structure, sourced predominantly from pipes in . This variety, historically prized for its rich tone resembling true , often occurs in larger crystals compared to other pyropes, enhancing its appeal in faceted gems. Rhodolite emerges as a hybrid variety blending pyrope with , typically comprising 75-90% pyrope component, resulting in a distinctive due to the iron content from almandine. This subtype, first identified in but now mined in locations like and , offers a lighter, more vibrant alternative to pure pyrope, with the purple tint arising from the balanced magnesium-iron substitution in its . Among other notable varieties, chrome pyrope stands out for its vivid, ruby-like red to violet-red shades imparted by chromium traces (3-8% Cr₂O₃), occasionally exhibiting subtle green undertones under specific lighting. Sourced from anthill deposits and , this chromium-enriched pyrope provides exceptional color intensity without the need for treatments. While pyrope varieties are overwhelmingly red, rare green garnets such as uvarovite—caused by in a calcium-based structure—belong to a distinct species and are not considered subtypes of pyrope.

Distinctions from Other Garnets

Pyrope differs from , another common red , primarily through its higher magnesium-to-iron (Mg/Fe) ratio in the , where pyrope is dominated by Mg₃Al₂(SiO₄)₃ while is Fe₃Al₂(SiO₄)₃. This compositional distinction results in pyrope having a lighter specific gravity of about 3.58, compared to 's heavier 4.1, which increases with iron content. Additionally, pyrope exhibits a purer, blood-red color without the brownish-red or purplish undertones often seen in due to higher iron influence. In contrast to , pyrope lacks significant content, the key element in spessartine's Mn₃Al₂(SiO₄)₃ formula that produces its characteristic orange to yellowish-orange tones. This absence of in pyrope ensures no orange hues and contributes to a more uniform around 1.74, narrower and lower than spessartine's variable range of 1.80 to 1.82. Most gems sold as pyrope are not pure end-members but solid solutions in the pyrope-almandine series, typically comprising 70-90% pyrope component with the balance , which subtly shifts properties like color and toward intermediate values.

Applications

Gemological Uses

is primarily used as faceted gemstones in modern jewelry, such as rings, necklaces, earrings, and pendants, where its hue provides an affordable alternative to more expensive red gems like . Fine-quality pyrope garnets, particularly smaller stones under 2 carats, are valued for their accessibility, often priced under $100 per carat, making them popular for everyday and pieces. Common cutting styles for pyrope include brilliant round and emerald cuts, which maximize its color play and brilliance while accommodating inclusions typical to the species. Oval, , and shapes are also favored to enhance the stone's fiery appearance in jewelry settings. Most pyrope garnets are sold untreated, though has been applied in some cases, particularly to almandine-pyrope blends in the past, to improve clarity and reduce a grayish tone. As the traditional January birthstone, pyrope sees steady demand in birthstone jewelry, symbolizing passion and constancy. It also holds market appeal in reproductions of vintage Bohemian designs and men's jewelry, where its durability supports robust settings like signet rings. With a Mohs hardness of 7-7.5, pyrope offers good wearability for such applications.

Industrial and Scientific Uses

Pyrope serves as an abrasive material in industrial applications, including the production of and use in waterjet cutting, leveraging its of 7 to 7.5 on the to effectively grind and cut various substrates. Despite these properties, pyrope is less commonly utilized for abrasives than , which dominates the market due to its abundance and similar durability. Almandite-pyrope solid solutions are among the more effective garnet types for such purposes, but pure pyrope sees limited adoption in these sectors. In scientific research, pyrope acts as a key indicator mineral in geothermobarometry for studying mantle conditions, particularly in peridotites, where its content and exchange reactions with coexisting phases like enable estimation of and in the lithospheric mantle. For instance, partitioning between pyrope and serves as a reliable geothermometer for equilibrated mantle xenoliths, providing insights into thermal gradients at depths exceeding 100 km. Chrome-pyrope xenocrysts from kimberlites further aid in reconstructing paleogeotherms through analysis of their major and compositions. Synthetic pyrope is synthesized under high-pressure conditions to simulate environments and investigate behavior in Earth's interior. These experiments, conducted using piston-cylinder or multi-anvil apparatuses at pressures up to 13 GPa, reveal pyrope's role in phase stability and water solubility, with applications in modeling deep-Earth dynamics and thermoelastic properties. First-principles calculations complement these syntheses, quantifying pyrope's elasticity and thermodynamic responses to pressures beyond 100 GPa.

Identification Methods

Gemological Testing

Gemological testing of pyrope begins with , which reveals a uniform deep color typical of this magnesium-rich variety, lacking the brownish tones often seen in almandine mixtures. Unlike anisotropic gems, pyrope exhibits no when viewed through a dichroscope, confirming its isotropic nature as a cubic . This single color appearance aligns with expectations for pyrope's optical characteristics, where the red hue stems from trace iron without directional color shifts. Specific gravity testing via provides a key identifier, yielding values typically between 3.62 and 3.87 for natural pyrope, depending on minor compositional variations such as content. yields a single refractive index reading around 1.74 to 1.76, with no observed, further distinguishing pyrope from doubly refractive gems. Under magnification, natural pyrope often displays characteristic inclusions such as needles, which appear as fine silk-like patterns, or healed fractures indicating pressures. These internal features, visible at 10x or higher, help verify authenticity in gem trade settings, as synthetic or imitation materials rarely replicate such natural imperfections.

Advanced Analytical Techniques

Advanced analytical techniques provide precise methods for confirming pyrope's composition and distinguishing it from other garnet species through spectroscopic and crystallographic analyses. Ultraviolet-visible-near infrared (UV-Vis-NIR) reveals characteristic absorption bands in pyrope, particularly those associated with trace elements like and iron. In Cr-bearing pyrope, a broad absorption band appears between 410 and 430 nm due to Cr³⁺ transitions, contributing to color variations, while the Fe²⁺ d-d transition produces a prominent band centered around 570 nm, which is a key signature for pyrope's red hue in natural samples. These bands, observed in polarized single-crystal spectra, allow quantification of iron oxidation states and help differentiate pyrope from iron-richer , where Fe²⁺ bands shift slightly to longer wavelengths. Raman spectroscopy offers a non-destructive way to identify pyrope's vibrational modes, focusing on the silicate framework. The spectrum of pyrope exhibits a strong peak at 910 cm⁻¹ attributed to the symmetric Si-O stretching vibration (ν₁ mode) of the SiO₄ tetrahedra, which is diagnostic for the pyralspite series (pyrope-almandine-spessartine). Additionally, a peak at approximately 1050 cm⁻¹ corresponds to asymmetric stretching modes, enabling distinction from almandine, whose equivalent band shifts to higher wavenumbers (around 1060 cm⁻¹) due to greater Fe content disrupting the lattice symmetry. These peaks, measured with excitation wavelengths like 514 nm, provide compositional insights when integrated with peak intensity ratios, supporting rapid in situ analysis of inclusions or gems. X-ray diffraction (XRD) confirms pyrope's cubic crystal structure, essential for its classification within the garnet group. Single-crystal XRD data reveal a cubic lattice with Ia-3d (no. 230) and unit-cell parameter a ≈ 11.52 for end-member Mg₃Al₂(SiO₄)₃, with peaks such as (400) and (440) indexing to this . Deviations in lattice parameters, observed under high-pressure conditions, reflect solid-solution effects but maintain the overall cubic habit. Complementing XRD, electron microprobe analysis (EMPA) quantifies major element ratios, particularly Mg/Fe, where pyrope typically shows Mg/(Mg+Fe) > 0.75 in the dodecahedral site, confirming its magnesium-dominant nature and distinguishing it from Fe-dominant almandine (Mg/(Mg+Fe) < 0.25). EMPA spot analyses, with beam currents of 15-20 nA, yield precise wt% oxides for SiO₂ (≈44.7%), Al₂O₃ (≈25.3%), and MgO (≈30.0%), enabling end-member calculations without sample destruction beyond the probed volume.

References

  1. https://www.mindat.org/min-3321.html
  2. https://geologyscience.com/gemstone/pyrope-garnet/
  3. https://www.gemsociety.org/article/pyrope-garnet/
  4. https://www.gemrockauctions.com/learn/a-z-of-gemstones/pyrope
  5. https://www.forbes.com/sites/davidbressan/2016/03/31/the-origin-of-geological-terms-garnets/
  6. https://www.mindat.org/article.php/4121/Pyrope
  7. https://www.gia.edu/garnet-history-lore
  8. https://www.eas.ualberta.ca/eml/files/Garnet_nomenclature_2013_formatted.pdf
  9. https://4cs.gia.edu/en-us/blog/famous-gemstones-pyrope-garnet/
  10. https://www.gemselect.com/gem-info/pyrope-garnet/pyrope-garnet-info.php
  11. https://www.gemsociety.org/article/garnet-symbolism-legends/
  12. https://www.langantiques.com/university/learn-with-lang/garnet-the-unsung-gem-of-vintage-jewelry/
  13. https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/10.1002/jrs.70027
  14. https://gem-a.com/gem-hub/garnet-gemstones-antique-jewellery/
  15. http://webmineral.com/data/Pyrope.shtml
  16. https://www.alexstrekeisen.it/english/pluto/garnet.php
  17. https://www.gia.edu/gems-gemology/winter-2015-vanadium-chromium-bearing-pink-pyrope-garnet-characterization-quantitative-colorimetric-analysis
  18. https://www.mdpi.com/2073-4352/12/3/379
  19. https://www.handbookofmineralogy.org/pdfs/Pyrope.pdf
  20. https://rruff.geo.arizona.edu/doclib/am/vol77/AM77_512.pdf
  21. https://academic.oup.com/petrology/article/40/5/679/1537916
  22. https://www.gemsociety.org/article/select-gems-ordered-density/
  23. https://www.gia.edu/doc/Pastel-Pyropes.pdf
  24. https://rruff.geo.arizona.edu/doclib/hom/pyrope.pdf
  25. https://snr.unl.edu/data/geologysoils/birthstones/garnet.aspx
  26. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/pyrope
  27. https://sandatlas.org/garnet/
  28. https://www.gia.edu/doc/GG-WN18-Diamonds-from-the-Deep.pdf
  29. https://www.gia.edu/red-pyrope-garnets-bohemia-reading-list
  30. https://nmgs.nmt.edu/publications/guidebooks/downloads/61/61_p0221_p0229.pdf
  31. https://www.gia.edu/doc/Gem-Localities-of-the-2000S.pdf
  32. https://www.theassayhouse.com/index.php/articles/minerals-and-their-classic-localities/garnet-localities
  33. https://www.gia.edu/gems-gemology/fall-2019-madagascar-garnets
  34. https://www.mindat.org/loc-1026.html
  35. https://www.ssef.ch/wp-content/uploads/2018/03/1987_Haenni_Garnets_-_a_colourful_gemstone_family.pdf
  36. https://www.gemsociety.org/article/rhodolite-garnet/
  37. https://www.gemsociety.org/article/uvarovite-garnet/
  38. https://www.gia.edu/garnet-description
  39. https://www.gemsociety.org/article/almandine-garnet/
  40. https://www.gemsociety.org/article/garnet-buying-guide/
  41. https://www.gemsociety.org/article/understanding-garnets-simplified/
  42. https://www.gemstonemagnetism.com/garnets_pg_2
  43. https://www.gemsociety.org/article/how-gems-are-classified/
  44. https://www.gemselect.com/pyrope-garnet/pyrope-garnet.php
  45. https://digital.library.unt.edu/ark:/67531/metadc12435/m2/1/high_res_d/Bulletin0256.pdf
  46. https://apps.usgs.gov/minerals-information-archives/gemstones/sp14-95/garnet.html
  47. https://pubs.geoscienceworld.org/rgg/article/47/10/1071/591918/EMPIRICAL-GARNET-THERMOBAROMETER-FOR-MANTLE
  48. https://www.sciencedirect.com/science/article/pii/S0024493724000252
  49. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/95JB03207
  50. https://www.sciencedirect.com/science/article/abs/pii/S0009254197001794
  51. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016JB013026
  52. https://www.gia.edu/garnet-quality-factor
  53. https://pubs.geoscienceworld.org/msa/ammin/article/108/6/1171/623656/Single-crystal-UV-Vis-absorption-spectroscopy-of
  54. https://pubs.geoscienceworld.org/msa/ammin/article-abstract/87/2-3/312/134028/Raman-spectroscopic-study-of-garnet-inclusions-in
  55. https://www.mdpi.com/2075-163X/12/12/1578
  56. https://www.sciencedirect.com/science/article/abs/pii/S1386142508006458
  57. https://next-gen.materialsproject.org/materials/mp-6073
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