| has gloss | eng: Spar is a term that is used to refer to a category of crystals that have readily discernible faces. Crystallized, earthy, and some metallic, a spar will easily break into rhomboidal, cubical, or laminated fragments with polished surfaces, but without regard to the ingredients of which they are composed. Amongst miners the term is frequently used alone to express any bright crystalline substance. Most frequently, spar describes easily cleaved, lightly colored nonmetallic minerals such as feldspar, calcite or barite. Barite (BaSO4), the main source of barium, is also called "heavy spar" (Greek "barys" means "heavy"). The largest type of spar is of the phreatic variety, since it essentially much more time to grow than average spar. It grows best where the water is just barely saturated with minerals. Some caves are like giant geodes, the walls and ceilings completely lined with spar. Jewel Cave and others in the Black Hills of South Dakota contain large quantities of spar. Minerals in the water, mostly calcite or gypsum, but sometimes even halite, quartz, and fluorite, are deposited through the course of thousands of years, building up on each other. |
