Diamond, at 10, is at the top of the Mohs scale. These crystals are massive rhombohedral in form. No matter what its color, its streak is white. Luster is vitreous to resinous to dull in massive forms. 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 .