Twinning also produces penetration twins that look like two cubes grown together. Cleavage is perfect in 4 directions forming octahedrons. Fracture is irregular. Hardness is 4. Streak is white.
Tenacity is brittle.
Group falls under the Halides. Often fluorescent blue or more rarely green, white, red or violet and may be thermoluminescent, phosphorescent and triboluminescent. Associated minerals are many and include calcite, quartz, willemite, barite, witherite, apatite, chalcopyrite, galena, sphalerite, pyrite and other sulfides. Industrial Uses Most of the fluorite mined in the world is used as a flux in the manufacturing of steel and other metals to eliminate impurities. There is large demand for fluorite in the optics field and to meet the demand fluorite is made synthetically.