FAQ
What is specific gravity?
Specific gravity is the ratio of a mineral density to water. Galena (7.58) is very dense, quartz (2.65) is average.
What is streak?
Streak is the color of a mineral powder when rubbed on unglazed porcelain. Often more reliable than color for identification.
What is cleavage?
Cleavage is the tendency of a mineral to break along flat planes of weak atomic bonding. Mica has perfect cleavage in one direction.
What is luster?
Luster describes how light reflects off a mineral surface. Main types: metallic, vitreous (glassy), pearly, resinous, adamantine (diamond-like).