Red grossular crystals in rodingite. From Hunting Hill Quarry, Rockville, Maryland. Scale is in centimeters. (Photo by W. Cordua.)

Formula: Ca3Al2(SiO4)3. Isometric


Grossular is a member of the garnet family found as pale white, green or tan crystals, most often in marbles, calc-silicate and other metamorphic rocks formed from calcium rich protoliths.

MARATHON COUNTY: Small light gray crystals up to 3 mm. in diameter are reported in several dikes in the northern section of the Wausau Pluton, near Wausau. (Falster, 1987).
— Yellow-brown garnets of unspecified composition are locally found in bedrock near Artus Creek at the NW NE sec. 29 T.29N. R.6E. (LaBerge and Myers, 1983). LaBerge and Myers speculate that these may be due to contact metamorphism by the nearby Wolf River Batholith. The color suggests these garnet may belong to the grossular-andradite series.

ONEIDA COUNTY: Grossular occurs with scapolite, diopside, tremolite and calcite in veins and intensely altered volcanic rocks at the Pelican River massive sulfide deposit in sec. 29 T.36N. R.9E., east of Rhinelander. (Bowden, 1978).
— Grossular is wide-spread in the calc-silicate rocks of the Lynn massive sulfide deposit, where it is associated with diopside, epidote and tremolite. (Kennedy, et al., 1991).

WOOD COUNTY: Grossular is reported as tiny grains in quartz at the Tork Quarry and Haesseley Quarry, both in Stevens Point. (Buchholz, 1996)