Grossular (variety of Garnet)
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Grossular is named from the Latin "Ribes Grossularium", the botanical name for "gooseberry" in reference to its typical greenish color because the original specimens were this color.

Discovered in 1811; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Ca₃Al₂(SiO₄)₃

Calcium Aluminum Silicate

Molecular Weight:

450.45 gm

Composition:

Calcium

26.69 %

Ca

37.35 %

CaO

Aluminum

11.98 %

Al

22.64 %

Al₂O₃

Silicon

18.71 %

Si

40.02 %

SiO₂

Oxygen

42.62 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/A.08-70

Nickel-Strunz 10th Ed. ID:

9.AD.25

9 : SILICATES (Germanates)
A : Nesosilicates
D : Nesosilicates without additional anions; cations in [6] and/or greater coordination

Related to:

Garnet Group. Grossular-Hibschite Series. Grossular-Katoite Series. Grossular-Uvarovite Series. Pyrope-Grossular Series.

Varieties:

Chromian Grossular, Hessonite, Hydrogrossular, Magnesian Grossular, Manganoan Grossular, Plazolite, Rosolite, Tsavorite

Synonyms:

African Jade, Colophonite, Ernite, Garnet Jade, Gooseberry-Garnet, Grossular Garnet, Grossularite, Kalkthongranat, Kanelstein, Olyntholite, Pechgranat, Romanzovite, South African Jade, Tellemarkite, Transvaal Jade, Wiluite (of Severgin)

Crystal Data

Crystallography:

Isometric - Hexoctahedral

Crystal Habit:

Commonly in dodecahedra or trapezohedra, up to 15 cm, with striated faces. Also granular, compact, and massive.

Twinning:

None observed

Physical Properties

Cleavage:

None observed. Parting rarely observed on {110}.

Fracture:

Irregular/Uneven, Sub-Conchoidal

Tenacity:

Brittle

Moh's Hardness:

6.5 - 7.0

Density:

3.594 (g/cm³)

Luminescence:

Almost always non-fluorescent; may be a weak golden yellow under LW & SW UV.

Radioactivity:

Not Radioactive

Optical Properties

Color:

Yellow-Green, pale to dark Green; golden Yellow, Pink, Red, Orange, Brownish Red, Yellowish Brown; Colorless, White, Gray, Black; may be sectored: Colorless in thin section.

Transparency:

Transparent to Opaque

Luster:

Vitreous, Sub-Vitreous, Resinous

Refractive Index:

1.731 - 1.754  Isotropic. RI increases with increasing iron contents (usually Fe3+).

Birefringence:

0.000 (Isotropic); may have weak strain birefringence of 0.0 - 0.005

Dispersion:

Strong

Pleochroism:

None

Occurances

Geological Setting:

In contact and regionally metamorphosed calcareous rocks, or rocks which have undergone calcium metasomatism; in some schists and serpentinites.

Common Associations:

Calcite, Dolomite, Epidote, Clinozoisite, Wollastonite, Scapolite, Vesuvianite, Diopside, Tremolite, Quartz.

Common Impurities:

Fe, Cr

Type Locality:

Akhtaragda River mouth (Achtaragda River mouth), Vilyui River Basin (Vilui River Basin; Wilui River Basin), Saha Republic (Sakha Republic; Yakutia), Eastern-Siberian Region, Russia

Year Discovered:

1811

View mineral photos:

Grossular Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Grossular, also known as Grossularite, is a member of the Garnet Group of minerals that includes Almandine, Andradite, Grossular, Pyrope, Spessartine and Uvarovite. The name Grossular is derived from the botanical name for the gooseberry, Ribes Grossularium, in reference to the green variety of Garnet that was originally found in the Vilyui River Basin, Eastern-Siberian Region, Russia. Other shades of Grossular include cinnamon-orange to brown, red, and yellow.

The more common variety of Grossular is called Hessonite from the Greek word "hesson" meaning "inferior", because of its inferior hardness to other varieties of Garnet. Hessonite Garnets range in color from cinnamon-brown to orange and have been called the "Cinnamon Garnet" because of its color. The color is due to the addition of iron to its chemical formula. Gem quality Hessonite is found in Sri Lanka, Tanzania, Brazil and California, USA.

Another variety of Grossular is the very highly sought after deep green Grossular known as Tsavorite. It was discovered in 1971 by British gem prospector and gemologist Campbell R. Bridges. The name Tsavorite was proposed in 1974 by Tiffany and Company president Sir Henry Platt in honor of the Tsavo National Park in Kenya were Bridges discovered it. Tsavorite's deep green color is due to trace amounts of vanadium or chromium.

Rosolite, also known as Rose Garnet or Xalostocite, is a rose-pink variety of Grossular from Sierra de la Cruz, Mun. de Sierra Mojada, Coahuila, Mexico.

Viluite is another variety of Grossular that is not very well know. It is usually olive green though sometimes brownish or reddish and comes from the Wilui River Basin area of Eastern Siberia, Russia.

Hessonite, Tsavorite, Rosolite and Viluite are varieties of Grossular and are not recognized as distinct mineral species. Grossular has also been given nicknames such as African Jade and Transvaal Jade.

Grossular Garnets are found at many localities, even for fine crystals and gem material. In Russia, near Chernyshevsk, at the confluence of the Vilyui and Akhtaragda Rivers, Yakutia. In the Ala Valley, Piedmont, Italy. From the Zillertal, Tirol, Austria. At Ocna de Fier, Romania. In the Jeffrey mine, Asbestos, Quebec, Canada. In the USA, at Standish, Cumberland County, Maine, and at the Belvidere Mountain quarries, Lowell, Orleans County, Vermont. In California, from Crestmore, Riverside County, the Old Cosumnes copper mine, El Dorado County, San Carlos mine, Mazourka Canyon, Inyo Range, Inyo County, and Santa Rosa, Sonoma County; on Vesper Peak, Sultan basin, Snohomish County, Washington. In Mexico, large crystals from Xalostoc and Morelos, Chihuahua, and from the Sierra de la Cruces, near Lake Jaco, Coahuila. Gems from the Merelani Hills, southeast of Arusha, Tanzania. In the Taita Hills, near Voi, Kenya.
 

  
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