Commonly occurs as small, flat, thin plates , as well as prismatic and tabular crystals.
Crystals frequently twin to form interesting results, such as heart, star, and v-shaped twins.
An oddity is reticulated growths of thin crystals which form a delicate, snowflake-like mass. Crystal faces are usually striated . Also occurs massive , fibrous , reticulated , acicular , radiating , coxcomb , and in wheat-sheaf form. A common form is encrustations of groups of small, fragile needles. Transparency Transparent to translucent Specific Gravity 6.5 - 6.6 Luster Greasy to adamantine.