COBALTITE
Cobaltite is an important cobalt ore mineral having
the formula (Co,Fe)AsS - cobalt iron arsenic sulfide. It's essentially
arsenopyrite with cobalt. Cobaltite has a metallic luster, a bright
silvery color, a dark gray streak, and is moderately hard (H = 5.5). It
can form cubic and pyritohedral crystals (the same crystal forms as pyrite),
but cobaltite has cleavage, unlike pyrite. It frequently occurs as finely
granular masses mixed with other minerals (see below). Cobaltite occurs
in some hydrothermal veins, and in some contact metamorphic rocks.
Cobaltite (silvery-colored) mixed with calcite (whitish-grayish) (4.3 cm across
at its widest).