Mineral name:  Fluorite Chemical formula:  CaF2 Location:  Cave-In-Rock, Hardin County, Illinois Crystal system and class:  Isometric  4/m32/m Genesis:  Fluorite is a commonly occurring hydrothermal vein mineral, either as the major mineral or as a gangue (valueless) mineral with metallic ores, especially lead and silver ores.  This specimen came from one of the Mississippi Valley Type hydrothermal deposits, in which it occurs with galena and sphalerite.  Fluorite is common in dolomites and limestones, and also occurs as a minor accessory minerals in some igneous rocks and pegmatites together with cassiterite, topaz, tourmaline, and apatite.  Fluorite occurs with a large number of other minerals, including calcite, dolomite, gypsum, celestite, barite, quartz, galena, sphalerite.  Width x length of specimen in cm:  11 x 12 Specimen number:  B790