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Grossularite Mineral Facts:

Chemical Formula: Ca3Al2(SiO4)3
Calcium aluminum garnet. Often contains ferrous iron replacing calcium and ferric iron replacing aluminum.

Colors: Colorless, white, green, yellow, orange, cinnamon-brown, pale red and occasionally pink.
Pure specimens are colorless. Colored varieties contain impurities such as iron, vanadium, manganese and other elements which give this garnet its color.

Hardness: 7

Density: 3.4 to 3.6

Cleavage: None.

Crystallography: Isometric, hexoctahedral
Usually distinctly crystallized; also in rounded grains; massive granular, coarse or fine. When crystalized, commonly forms dodecahedron and trapezohedron, often in combination. Hexoctahedron observed at times.

Luster:Vitreous glassy luster. It is transparent or translucent. 

Optics: (Refractive Index):  = 1.7438

Grossularite Garnet

Grossularite Garnet, Nevada

Composition, Structure and Associated Minerals:
Grossular, with its Calcium and aluminum content, is characteristic of metamorphosed impure limestones, in which it occurs associated with other lime silicates, idocrase, scapolite, etc. Grossularite is found chiefly as a product of contact or regional metamorphism in crystalline limestone especially where acidic rocks like granite are intruded into limestone.
Grossularite, Essonite, Hessonite, or Cinnamon Garnet occurs in crystalline schists and in metamorphosed limestones, where it is associated with other calcium silicates. It is found also in quartz veins.
The name derived from the botanical name for gooseberry, in allusion to the light green color of the original grossularite.

Under the influence of the air and moisture garnets often alters to other minerals, being partially or entirely changed to epidote, talc, muscovite, chlorite, serpentine, and occasionally to other substances.

Identification and Diagnostics
Fusible before the blowpipe flame. Garnets, when in crystals, are easily distinguished from other similarly crystallizing substances by their characteristic isometric crystals, color and hardness, etc. Massive garnet may resemble vesuvianite, sphene, zircon or tourmaline. It is distinguished from zircon by its easier fusibility and from vesuvianite by its more difficult fusibility; from tourmaline by its higher specific gravity, and from sphene by the reaction from titanium. It frequently requires a chemical analysis to positively distinguish between the different members of the group, or the percentages of each molecule in an individual specimen

Occurrence, Localities and Origins:
The mineral is white, bright yellow, cinnamon-brown or some pale shade of green or red. The lighter-colored varieties are often transparent or nearly so. Those that are both transparent and well colored are used as gems. Much of the hyacinth of the jewelers is an orange to red colored grossularite.  The best known historical source of gem hessonite is Sri Lanka, where it occurs in the gem gravels, notably in the Matura district.

In recent decades, large amounts of fine gem quality grossular garnet has come from Africa, principally Tanzania and Kenya. Some are orange colored, another source produces pale yellow, near colorless and light green varieties. However the best known variety of this garnet is the Tsavorite, a medium to deep green garnet colored by vanadium.  Tsavorite has become the most valuable garnet type with a high price per carat for good quality stones. Its color comes close to that of a fine emerald with brighter optical characteristics and without the typical flaws. 

Good crystals of grossularite occur at Phippsburg, Raymond and
Rumford, in Maine, and at many other places both in this country and abroad. Bright yellow varieties are reported from Canyon City, Colorado

Return to the Mineral Collectors Information Page

Grossular Garnet, Variety Tsavorite

Grossular Garnet, Variety Tsavorite

Pink Grossularite Garnet

Pink Grossularite Garnet


Please note that the author, Chris Ralph, retains all copyrights to this entire document and it may not be reproduced, quoted or copied without permission.

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