Perfect in three directions, forming rhombohedrons. Fracture is conchoidal. In Olmstead County, calcite forms the major portions of hydrothermal veins that occur in the limestone. In this environment, pyrite, a metal sulfide, can be an associate mineral. This mineral forms short, prismatic crystals, often as cruciform twins.
Fracture is uneven to conchoidal.
Staurolite is a common metamorphic mineral that is useful to geologist to determine the degree of metamorphism of aluminum-rich rocks and is found in schists and gneiss . It occurs in Benton County near the town of Royalton. Associated minerals include micas and other metamorphic minerals. It varies from colorless to white, gray or silver, and it may be tinged with yellow, green, or brown. It is a transparent to translucent mineral, with a vitreous to pearly Luster .