Minerals · common

Grossular

Grossular is the calcium aluminum member of the garnet group, Ca3Al2(SiO4)3, notable for its unusually broad color range that spans colorless, green, yellow, orange, red, and brown depending on trace element substitutions. It forms characteristically in calcium-rich metamorphic rocks such as skarns and impure marbles, where it crystallizes during contact or regional metamorphism. Its name derives from the botanical genus for gooseberries, referencing the pale green color of the type specimens from Siberia.

Photo: Robert M. Lavinsky · Wikimedia Commons · CC BY-SA 3.0

Grossular properties at a glance

Type	Minerals
Chemical formula	Ca3Al2(SiO4)3
Mohs hardness	6.5–7.5
Crystal system	Cubic
Luster	Vitreous to resinous
Streak	White
Cleavage	None
Fracture	Conchoidal to uneven
Specific gravity	3.4–3.8
Transparency	Transparent to translucent
Common colors	Colorless, Green, Yellow, Orange (hessonite), Brown, Pink
Rarity	common

Geology & background

Grossular forms primarily through contact metamorphism, when calcium-rich limestones or dolomites are altered by heat and fluids from an intruding magma body, producing skarn zones where grossular crystallizes alongside vesuvianite, wollastonite, and diopside. It also occurs in regionally metamorphosed calc-silicate rocks and, less commonly, in ultramafic-derived rodingites. Major sources include Kenya and Tanzania's tsavorite-producing marbles, Mexico's Xalostoc deposits famous for orange hessonite garnet, Quebec's Jeffrey Mine for hydrogrossular, and Pakistan's Gilgit-Baltistan region for fine green and orange crystals.

Collectors highly value grossular for its gemological varieties, particularly tsavorite, a vivid chrome- and vanadium-colored green prized as a gemstone, and hessonite, a cinnamon-orange to reddish-brown variety long used in antique jewelry. Well-formed dodecahedral or trapezohedral crystals in skarn matrix are desirable specimens, and the mineral's wide color range means a single collection of grossular can showcase considerable visual diversity while remaining chemically consistent.

How to identify Grossular

Grossular's color varies dramatically from colorless and pale green to vivid tsavorite green, honey-yellow, cinnamon-orange hessonite, and reddish-brown, all sharing a vitreous luster and white streak. It has a hardness of 6.5 to 7.5, no true cleavage, and typically forms rounded dodecahedral or trapezohedral crystals in marble or skarn, sometimes as massive material resembling jade when compact and fine-grained. Grossular can be confused with other garnet species like andradite or spessartine, and its massive green form is sometimes mistaken for jade, but its crystal habit, hardness, and skarn or marble host rock help confirm the identification.

Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
Use multiple photos when possible, including a fresh surface and a close view of texture.

Where Grossular is found

Reported from multiple localities worldwide; verify locality against specimen provenance when available.

How much is Grossular worth?

Entry-level specimen	$2
Typical collector specimen	$20
Premium specimen	$150+

Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.

Common uses

Collector specimens
Education
Field identification
Industrial or lapidary use when suitable

Interesting facts

Tsavorite, the vivid green variety of grossular garnet, was discovered in Tanzania in 1967 and named after Kenya's Tsavo National Park near where it was later also found.
Massive, fine-grained green grossular is sometimes sold as "Transvaal jade" because it can closely resemble true jade in appearance and polish.
Grossular gets its name from the botanical genus Ribes, better known as gooseberries, because early specimens from Siberia resembled the pale green fruit.