Grossular Garnet: Gemstone Information
Name Grossular garnet approved by the CNMMN of the IMA. Synonyms are grossularite, hessonite, essonite, cinnamon stone, rosolite, tsavorite, tsavolite, wiluite and mali. Color varieties are hessonite (orange-brown), tsavorite (green) and mali (yellowish green to greenish yellow), leuco-garnet (colorless), imperial garnet (light pink), raspberry garnet (raspberry red), gooseberry garnet (gooseberry-green), tangerine garnet (bright orange), merelani (mint-green). ‘Grandite’ is the term that has been applied to grossular garnets with significant, although normally less than 50%, andradite molecule. Grossular is so named in allusion to the resemblance of pale green specimens to the gooseberry (Ribes grossularia).
Occurrence
Grossular is especially characteristic of both contact (skarns) and regionally metamorphosed impure calcareous rocks or rocks that have undergone calcium metasomatism. It also occurs in association with serpentinites and rodingites. Additionally as detrital grains in placers deposits. Notable localities for gem-quality grossular include Sri Lanka (hessonite), India, Tanzania (tsavorite, hessonite), Kenya (tsavorite), Mali, Namibia, Madagascar (hessonite), Pakistan, Russia (chrome-grossular), Italy, USA (California), Canada, Mexico and Brazil. Massive material similar in appearance to hydrogrossular occurs at: Yukon, Canada; California and other states in the USA; Myanmar; and South Africa.
Properties
Grossular Garnet forms a series with andradite and uvarovite, and also the hydrogarnets. Moreover, solid solution to varying extent occurs with the pyralspite series. Consequently the physical and chemical properties and
appearance can vary appreciably.
Refractive Index
The RI of ugrandite garnets is strongly dependent on the calcium content, but does not vary significantly with changes in the Fe3+: Cr3+ ratio.
The calculated value of the end-member is 1.732; however, actual values will vary due to isomorphous replacement and measured literature values for 50% 100% grossular range from 1.796 to 1.737 respectively based on predominant andradite substitution.
Mali: 1.770 (greenish yellow); 1.768 (brownish yellow)
Mali pale greenish yellow: 1.739–1.750
Colorless Mali grossular: 1.742–1.751
Emerald-green grossular (Bekily, Madagascar): 1.741–1.746
Gogogogo, Madagascar: 1.742
Manson and Stockton study of 105 grossular garnets gave range from 1.731 to 1.754.
Refractive index values for African tsavorite range between 1.739 and 1.744 whilst that Swat material is 1.743.
Hessonite from Paskema and Okkampitiya, Sri Lanka, ranges from 1.731 to 1.735.
Specific Gravity
Mali: 3.66 (greenish yellow); 3.64 (brownish yellow)
Mali pale greenish yellow: 3.61–3.63
Emerald-green grossular (Bekily, Madagascar): 3.58–3.62
Gogogogo, Madagascar: 3.62
Manson and Stockton study of 105 grossular garnets gave range from 3.57 to 3.67.
African tsavorite values range from 3.57 to 3.65 and that of Swat material is 3.64.
Hessonite from Paskema and Okkampitiya, Sri Lanka, ranges from 3.598 to 3.622.
Hardness Tsavorite -7.25
Color
Grossular garnets range from colorless (rare) through hues, shades and various tints of brown, yellow, orange and green. Mali, West Africa, for example, has provided gemmy rough in a range of colors including dark brown, orangey brown, light yellowish brown, yellowish green, light peridot-green, olive-green and intense bluish green. A direct correlation exists between increasing green tone and vanadium concentration; however, chromium, even in very low concentrations, can have significant effect on the green coloration. With increasing Fe3+, color changes from yellow through orange to orange-red.
Color varieties:
Tsavorite
Originally discovered (1967) and described from the Tsavo National Game Park in Kenya from which it took its name, this green vanadium-bearing (goldmanite component) grossular garnet, with minor chromium, is more
prevalent in Tanzania where production from Tunduru, Ruangwa, Umba, Merelani Hills and Komolo has outstripped that from Kenya. Also found at Gogogogo, Madagascar. Colors range from bluish green to yellowish green, the former, sometimes called forest green, being the most highly regarded. Tsavorite is uncommon in sizes above 3 ct.
Vanadian grossular has also been reported from Swat, Pakistan. Meralani Mint Green This is the trade name for bright green garnet discovered in the same mines that produce Tanzanite, about 25 miles south-east of Arusha,
Tanzania. It is essentially a light colored tsavorite.
Hessonite
Hessonite is the name given to the yellow orange to brownish orange color variety. The color is attributed to traces of iron. Major localities are Sri Lanka and India. Lighter oranges, yellows and peachy-colored stones occur in deposits in Alberta and Quebec, Canada. Other localities include Mexico, Brazil, Tanzania and Madagascar.
Leuco Garnet
(colorless) Leuco garnet is the name that is normally applied to the colorless, transparent variety of grossular that usually contains 2% iron. Main occurrences are Sri Lanka and Quebec, Canada.
Tangerine Grossular
This is the trade name for bright orange garnet, sometimes confusingly termed ‘mandarin’ grossular that has been found as water-worn alluvial pebbles from the Ruvuma River, Tanzania. Orange grossular from Tanga has been confusingly termed ‘malaya’.
Mali
In September 1994 a new deposit of garnet was discovered in the republic of Mali, in Western Africa. At first identified as chrysoberyl on the basis of color, it was later found to be a combination of andradite and grossular (Gr80An20). The bright colors range from chartreuse to a yellow-green to an almost honey green. A rare chrome green color has also been reported.
Inclusions
Apatite inclusions are common and calcite has been reported from a number of localities. Hessonites usually have a characteristic grainy and/or swirly internal appearance known as ‘treacle’: latest examinations show that this is the result of a mosaic structure caused by intergrown hessonite grains. Scapolite inclusions have been reported in massive hessonite from Maligawila, Sri Lanka, and also from Lelatema, Tanzania. Lamellar growth structures in Mexican hessonite produce iridescent colors similar to that reported for Mexican andradite. In tsavorite, fingerprint and geometric patterns arising from tiny droplets, negative crystallites and solid particles are reported. Additionally, graphite scales and asbestiform actinolite fibres have been observed.
Optical Effects: Chatoyancy, Asterism, Color Change, ADR
Ultraviolet Fluorescence: some green garnets (grossular and tsavorite) may show a weak orange in LWUV and weak yellow in SWUV. A color shift has been reported from Mali garnets: under incandescent light they have a more yellow tint, and in daylight they a
re more green.
Treatment
Some colorless to pale tone grossular from various localities in East Africa will turn light yellow-green when irradiated (gamma rays) but will fade to their original color within hours to days in daylight and within two months in the dark. These are characterized by a transmission window near 560 nm. Some material has been dyed green to imitate jadeite; this shows an absorption band from 630 to 670 nm and red under the Chelsea Color Filter.
Exploring the Beauty and Benefits of Grossular Garnet
Introduction:
Grossular garnet, a gemstone renowned for its diverse colors and exceptional beauty, has captivated gem enthusiasts for centuries. Named after the botanical term “grossularia,” meaning gooseberry, this gemstone comes in a variety of colors, ranging from green to yellow, orange, and pink. In this article, we’ll delve into the origins, properties, uses, and benefits of Grossular garnet, shedding light on why it remains a cherished gemstone among collectors and jewelry enthusiasts worldwide.
Origins and Characteristics:
Grossular garnet belongs to the garnet group of minerals and is composed of calcium aluminum silicate. It is typically found in metamorphic rocks, particularly in regions with significant geological activity such as contact metamorphism or regional metamorphism. Grossular garnet crystals can vary in color depending on their chemical composition, with the green varieties often containing traces of chromium or vanadium, while the yellow to orange varieties may have manganese or iron impurities. This gemstone is found in various locations worldwide, including Africa, Canada, and the United States.
Properties and Features:
One of the most notable features of Grossular garnet is its exceptional brilliance and luster, which rivals that of more well-known gemstones like emerald or ruby. Grossular garnet crystals often exhibit transparency and clarity, with some specimens displaying asterism, a phenomenon where a star-like pattern appears when light is reflected off the surface of the gemstone. Additionally, Grossular garnet has a relatively high hardness, ranging from 6.5 to 7.5 on the Mohs scale, making it suitable for use in jewelry.
Varieties and Colors:
Grossular garnet occurs in a variety of colors, each with its own unique characteristics and appeal. The green variety, known as “grossularite,” is prized for its deep green hues reminiscent of jade. The yellow to orange varieties, known as “hessonite,” often display warm, honey-like tones that evoke feelings of warmth and vitality. Additionally, Grossular garnet may occur in pink or reddish hues, known as “rosolite,” which are prized for their delicate beauty and rarity.
Uses in Jewelry:
Grossular garnet’s diverse colors and exceptional brilliance make it a popular choice for jewelry designers and enthusiasts alike. It is often faceted or cut into cabochons for use in earrings, pendants, necklaces, and rings, where its vibrant colors can be showcased and appreciated. Grossular garnet is also a favorite among collectors, who seek out fine specimens with exceptional color, clarity, and size to add to their collections.
Metaphysical Properties:
In addition to its aesthetic appeal, Grossular garnet is believed to possess various metaphysical properties that promote emotional healing, balance, and vitality. It is often associated with the heart chakra, encouraging feelings of love, compassion, and harmony. Some practitioners of crystal healing also believe that Grossular garnet can enhance creativity, stimulate the imagination, and promote a sense of abundance and prosperity.
Healing Benefits:
Grossular garnet is associated with various healing properties that are said to benefit both the body and the mind. It is believed to support the immune system, aid in detoxification processes, and promote overall well-being. Grossular garnet is also said to alleviate symptoms of depression, anxiety, and stress, helping to restore emotional balance and inner peace. Additionally, Grossular garnet is thought to promote physical vitality and stamina, making it a valuable ally for those seeking to enhance their energy levels and vitality.
Collectibility and Rarity:
While Grossular garnet is relatively abundant compared to some gemstones, fine specimens with exceptional color and clarity are highly prized by collectors. Varieties such as the vivid green grossularite or the honey-colored hessonite are particularly sought after for their beauty and rarity. As with many gemstones, the value of Grossular garnet is influenced by factors such as size, quality, and provenance, with collectors often seeking out rare and exquisite specimens to add to their collections.
Conclusion:
In conclusion, Grossular garnet stands out as a gemstone of exceptional beauty, versatility, and metaphysical significance. From its diverse colors and exceptional brilliance to its healing properties and collectibility, Grossular garnet continues to captivate and inspire gem enthusiasts worldwide. Whether admired for its aesthetic appeal, valued for its metaphysical properties, or cherished as a collector’s item, Grossular garnet remains a cherished gemstone that embodies both elegance and vitality.