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Chemical Formula | Ca3Al2Si3O12 | ||
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Composition | Calcium aluminum silicate, commonly with some iron or chromium replacing some aluminum | ||
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Variable Formula | Ca3(Al,Fe3+,Cr)2Si3O12 | ||
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Color | Colorless, white, green, yellow, pink, brown, orange, orange-red. Some massive specimens may be multicolored white, light green, and pink. | ||
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Streak | Colorless | ||
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Hardness | 6½ - 7½ | ||
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Crystal Forms and Aggregates |
(Isometric) Most commonly as dodecahedrons, and occasionally as trapezohedrons. Also occurs in crystal clusters, massive, in vein-like masses, and in many small, single crystals on a matrix. | ||
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Transparency | Transparent to translucent | ||
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Specific Gravity | 3.6 | ||
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Luster | Vitreous | ||
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Cleavage | None | ||
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Fracture | Conchoidal to uneven | ||
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Tenacity | Brittle | ||
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Other Names |  Grossularite, Wiluite |
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Varieties |  Hessonite - Orange to
orange-brown, transparent variety of Grossular Cinnamon
Stone or Essonite - Synonym of Hessonite
(above) Tsavorite
- Emerald-green, chromium-rich variety of Grossular Leuco-garnet
- Colorless, transparent variety of Grossular Rosolite
- Light pink variety from Morelos and Lake Jaco, Mexico South
African Jade - Massive veins of opaque Grossular resembling Jade.
It is white to light green in color, and may be admixed
white, green, and pink. African
Jade, Transvaal Jade, Garnet Jade - Synonym of
South African Jade (above) Hydrogrossular
- See HibschiteHibschite and Katoite are sometimes classified as a variety of Grossular, but they are scientifically separate minerals. |
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In Group | Silicates ; Nesosilicates ; Garnet group | ||
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All About | Grossular is a Garnet, belonging to the Garnet
group.
The Garnet group is a small group of closely related
minerals. The members of the Garnet group are isomorphous, and some of them freely
intermingle. They vary only slightly in physical
properties, and some of them may be so similar that they
are indistinguishable from one another without x-ray
analysis. The most common members are: Pyrope, Almandine, Spessartine, Grossular, Andradite, and Uvarovite. The minerals in the Garnet group are called "Garnets". All Garnets are hard and many are fit for gem use. Unless articulate, most mineral and gem dealers don't refer to garnets by their true name (i.e. Grossular), but by the name "Garnet". The garnets as a group occur in all colors (except for blue). For more information about garnets, see the Garnet group. Grossular is the most varicolored of all Garnets. It occurs in all colors except those of blue tints. It most often occurs in crystal groups on a matrix, although single crystals and rounded, waterworn pebbles have also been found. |
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Uses | Transparent Grossular is cut into gems. The
orange to orange-brown variety Hessonite is the most
famous gem of this mineral. Most cut Grossular gems are
known simply as "Garnets"or "Grossular
Garnet", except for Hessonite, which is known by its
own name in the gem market. The massive, veinlike material from South Africa is sometimes
carved into ornaments. Grossular is a valuable mineral to
collectors, and good specimens demand a high price. See the gemstone section on garnet |
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Striking Features | Crystal forms and hardness | ||
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Popularity (1-4) | 2 | ||
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Prevalence (1-3) | 2 | ||
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Demand (1-3) | 1 | ||
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Distinguishing Similar Minerals |
Spessartine - very hard to distinguish without
complex methods Andradite - very hard to distinguish without complex methods Uvarovite - usually darker green and in denser aggregates Tourmaline - lighter in weight, occurs in different crystals Vesuvianite - occurs in different crystals; otherwise difficult to distinguish Peridot - occurs in different crystals Analcite - softer |
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Commonly Occurs With |
Calcite, Wollastonite, Vesuvianite, Quartz, Diopside | ||
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Noteworthy Localities |
Perfect individual crystals are found in the
gem-bearing sands of Sri Lanka. Large, massive hunks from
Myanmar (Burma) were carved out by the ancient Chinese,
thinking it was Jade.
An emerald-green, chromium-rich variety occurs in
Tanzania and Kenya, and is commonly sold under the name
"Tsavorite". Large, veinlike masses are found
in South Africa. Grossular also occurs in Broken Hill,
New South Wales, Australia; Val D'Ala (Ala Valley),
Piedmont, Italy; Telemarken, Norway; Maharitra,
Madagascar; and Minas Gerais, Brazil. Some of the finest crystals come from the Jeffery Mine in Asbestos, Richmond Co., Quebec, Canada. Grossular crystals also occur in Gatineau and Magantic counties in Quebec. In Mexico, white and pink crystals are found in Morelos and Lake Jaco, Chihuahua. Perfect, white to light green dodecahedral crystals come from Sierra de las Cruces, Coahuila. In the U.S., it occurs in Minot, Androscoggin Co., Maine; Sanford, York Co., Maine; Warren, Grafton Co., New Hampshire; Eden Mills, Vermont; the French Creek mine, St. Peters, Chester Co., Pennsylvania; Milford, Beaver Co., Utah; the Seven Devils district, Adams Co., Idaho; and Havila, Kern Co., California. |
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Picture Icon Links |
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Picture Links | 1. Pink Grossular crystal |
