Andradite Garnet: Gemstone InformationÂ
The Name Andradite Garnet approved by the CNMMN of the IMA. Synonyms are allochroite, aplome, calcium-ferrigranat, polyadelphine and polyadelphite. Andradite Garnet is named after the Brazilian statesman and geologist Jose Bonifacio d’ Andrada e Silva (1763–1838), who first described the mineral.
Frequently found in metamorphosed limestones and metamorphosed impure carbonate-bearing rocks; particularly in metosomatic skarns. The light-colored andradite varieties topazolite and demantoid occur mainly in chlorite schists and serpentinites respectively. The darker andradite variety melanite and the related schorlomite occur mainly in alkaline igneous rocks such as nepheline syenites and phonolites. Andradite also occurs in metamorphosed igneous rocks, and additionally as detrital grains in placer deposits. Notable localities for gem-quality andradite include: Russia (Ural Mts), USA(Arizona), Namibia (Erongo Mts) for green (vanadium rich–chromium poor) andradite, some of which may be considered demantoid; Iran (Kerman), Afghanistan (Khost, Kunnar) and Pakistan (Kashmir) for demantoid; USA (California), Italy (Piedmont) and Switzerland (Zermatt) for topazolite; Greenland, Norway, Sweden, Germany, Uganda, Madagascar, Sri Lanka, Russia and Zaire for andradite of non-specific color variety or melanite. Semi-transparent light apple-green demantoid with significant grossular/ hydrogrossular content has been reported from Kamchatka and Chukotka, Soviet Union.
Andradite generally contains significant amounts of the grossular molecule, and a continuous isomorphous series exists between these two components. This has been termed the grandite series. A second series exists with schorlomite that includes melanite (titanium andradite). It is sometimes in solid solution with spessartine and uvarovite. Consequently the physical and chemical properties and appearance can vary appreciably.
Refractive Index
The calculated value of the end-member is 1.889. Actual values will vary due to isomorphous replacement and literature values for 50–100% andradite range from 1.82 to 1.89 respectively. Melanite, with its high titanium content, gives elevated RI values up to 1.97 where Fe3+ > Ti. Demantoid values are reported as ranging from 1.880 to 1.889; the higher value relating to dark-green material. Topazolite RIs ranging from 1.84 to 1.89 have been recorded for Alpine material.
Density
Pure end-member (calculated) 3.859. Extracting values from the literature, where chemical information is provided, indicates that for ugrandite garnets containing 50% andradite molecule the lower limit of density approximates to 3.77. Measured values for SG normally range from 3.82 to 3.85. It should be borne in mind that inclusions could affect measured density and, if in abundance, give rise to skewed values.
Hardness
Hardness on Mohs’ scale ranges from 6.5 to 7.5 with demantoid at the lower end of this range.
Dispersion
Very high at 0.057; greater than that of diamond (0.044) or titanite (0.051). The effect is partially masked by body color especially in intensely colored demantoid.
Appearance
Color
Occurs in various hues: red, brown, yellow (topazolite) and green (demantoid) and shades in between these; also as black (melanite). Also reported as colorless and grey. Tsavorite-like colored andradite has been reported from Madagascar. Color Varieties: Demantoid color arises from the presence of small amounts of chromium. Whilst the color of demantoid never approaches that of the finest emerald, favourable comparison can be made especially in vividly colored stones that are not overly dark or contain yellow hues.
Chemical analysis of demantoid from Kashmir, Pakistan, showed relatively pure andradites with 0.25 wt% of Cr2O3. The demantoid from Panshir Valley, Kunnar, Afghanistan, is transparent but very dark green. The green andradite from Farm Tubussis, Erongo Mountains, Namibia, has only minor chromium but a significant vanadium content and is being traded as demantoid.
Topazolite
Topazolite was named after its similarity to yellow topaz but is now used to include also more orangey material. Some andradite from the Urals is a strong yellow component and is closer to topazolite than demantoid.
Melanite
Melanite is from the Greek word melanos meaning black, referring to its color. This opaque material was historically used for mourning jewelry, or as inlay.
Inclusions
Significant, and diagnostic when seen, are wispy, horse-tail like, fibrous inclusions of chrysotile (serpentine asbestos) inclusions that historically had been referred to as byssolite, a now obsolete term, or fibrous asbestiform actinolite. Seen in demantoid from Russia, Eritrea and Italy but not Namibia. Opaque chromite crystals may form the nucleation point for the chrysotile. Tiny fluid inclusions are seen in Namibian demantoid, also negative crystals with two phase inclusions and pronounced angular or straight transparent growth zoning which rarely may be iridescent (‘rainbow graining’). Acicular diopside crystals have been reported as inclusions in demantoid from the Urals.
Yellowish green to emerald-green demantoid from Kashmir, Pakistan, had acicular, fibrous and felt-like mineral inclusions that were identified as chrysotile. Partially healed fractures and liquid inclusions plus small unidentified needle-like inclusions and transparent crystals have been reported from andradite from the Yemen. Healed fractures, growth banding (best seen in polarized light) and two phase inclusions have been reported in Arizona andradite. Yellowish brown Namibian andradite had yellow needles.
Optical Effects: Chatoyancy, Asterism, Color Change, ADR
Iridescent andradite from Sonora, Mexico, is sometimes referred to as ‘rainbow garnet’. The iridescence is caused by cylindrically stratified growth lamellae in the {211} and {110} sectors. The stratification is between An79% and An94%. Green andradite from Farm Tubussis, Erongo Mountains, can often have an unappealing color shift towards brown in tungsten light. Some demantoid show a color change from yellowish green to a bright
sparkling pastell green (daylight). Rarely, some show a color change from green to orange.
Treatment
Color enhancement of demantoid has been achieved by heat treatment under reducing conditions. Brown and yellow hues are removed and green enhanced by converting some Fe3+ to Fe2+ Alferova M.S. pers comm.).
Title: Unveiling the Allure and Benefits of Andradite Garnet: A Comprehensive Guide
Introduction: Andradite Garnet, with its mesmerizing green hues and exceptional brilliance, stands as a testament to nature’s artistry and geological wonders. In this comprehensive guide, we delve into the captivating world of Andradite Garnet, exploring its origins, characteristics, and the myriad benefits it offers to gem enthusiasts and collectors alike.
Origin and Characteristics: Andradite Garnet belongs to the garnet group of minerals, which encompasses a diverse array of gemstones renowned for their vibrant colors and stunning clarity. Named after the Brazilian mineralogist José Bonifácio de Andrada e Silva, Andradite Garnet is distinguished by its rich green coloration, though it can also exhibit shades of yellow, brown, and black.
This exquisite gemstone is typically found in metamorphic and igneous rocks, often forming in association with minerals such as quartz, feldspar, and mica. It owes its captivating green hue to traces of chromium and iron within its crystal structure, which imbue it with a remarkable depth and intensity of color.
One of the most notable characteristics of Andradite Garnet is its exceptional brilliance and luster. When expertly cut and polished, it displays a mesmerizing sparkle that rivals even the finest diamonds, making it a highly coveted gemstone among connoisseurs.
Benefits and Uses: Andradite Garnet boasts a range of benefits that extend beyond its aesthetic appeal, making it a valuable addition to any gem collection. Here are some of the key advantages and uses of this exquisite gemstone:
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Healing Properties: Andradite Garnet is believed to possess various metaphysical properties that promote physical, emotional, and spiritual well-being. It is said to stimulate the root chakra, enhancing feelings of security, stability, and vitality. Additionally, Andradite Garnet is thought to alleviate stress, anxiety, and negative energies, fostering a sense of inner peace and harmony.
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Creativity and Inspiration: In the realm of creativity and inspiration, Andradite Garnet is revered for its ability to awaken the imagination and ignite a passion for artistic expression. It is believed to enhance creativity, intuition, and innovation, empowering individuals to manifest their dreams and aspirations with clarity and confidence.
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Protection and Grounding: Andradite Garnet is also associated with qualities of protection and grounding, serving as a shield against harmful influences and energies. It is said to provide a sense of stability and security, helping individuals navigate life’s challenges with resilience and fortitude.
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Jewelry and Ornamental Purposes: Beyond its metaphysical properties, Andradite Garnet is highly sought after for its stunning beauty and versatility in jewelry design. From exquisite rings and earrings to elaborate necklaces and bracelets, Andradite Garnet lends a touch of elegance and sophistication to any piece of jewelry. Its rich green coloration makes it particularly prized for statement pieces and heirloom-quality creations.
Conclusion: In conclusion, Andradite Garnet is a gemstone of unparalleled beauty and significance, cherished for its captivating green hues, exceptional brilliance, and myriad metaphysical properties. Whether adorning a piece of jewelry or serving as a source of inspiration and healing, Andradite Garnet continues to captivate the hearts and minds of gem enthusiasts around the world, embodying the timeless allure of nature’s treasures.
