Halides, nitrates, and borates are minerals that combine with the halogen elements, nitrogen, and boron. Examples include halite (salt), sylvite, fluorite, niter (saltpeter), borax, and kernite. Fluorite is very common in central and western Kentucky, whereas the borate minerals are not common in Kentucky.
Crystal system: isometric with cubic crystals, more often massive. Cleavage: excellent octahedral cleavage; may be broken into triangular-faced fragments. Color: white, purple, green, yellow, brown. Hardness: 4.0. Streak: colorless. Luster: glassy. Specific gravity: 3.18. Uses: flux, hydrofluoric acid, enamel and glass industries, refrigerating fluids, portland cement, insecticides, to retard tooth decay.
Fluorite is often called spar or fluorspar. Massive fluorite may resemble calcite, but it is heavier and does not effervesce when treated with hydrochloric acid. It is distinguished from gypsum and quartz by its hardness. The Kentucky-Illinois fluorspar area once was ranked first in the United States in the production of fluorite. In Kentucky, commercial deposits occur in Caldwell, Crittenden, and Livingston Counties. A small amount of noncommercial fluorite occurs in veins in the Central Kentucky Mineral District. Numerous mines and mine dumps along the Tabb and Commodore Faults in western Kentucky contain fluorite, and several mines near Mundys Landing in southern Woodford and northern Mercer County have produced nice fluorite specimens. Most of these mines are now closed. Many old uncovered shafts exist in the vicinity of old mines, so caution should be used when collecting near these areas because of open shafts.
One of the most outstanding collections of fluorite is the Clement fluorite collection, located in Marion, Kentucky. This collection consists of various specimens of fluorite collected by Mr. Ben Clement while he worked in the fluorspar district. Since most of the mines are now closed, a visit to this collection is the best way to view the beautiful colored fluorites.
Crystal system: isometric. Cleavage: commonly in cubes. Color: white. Hardness: 2.5. Streak: white. Luster: vitreous. Specific gravity: 2.25.
Halite, also known as common table salt, has a strong salty taste, which is the most diagnostic tool for identification. Although not common in Kentucky, it does occur in brine waters, salt springs, and salt licks. It can be formed as encrustations and small crystals at salt licks. Prehistoric animals walked miles to salt springs and licks to obtain this chemical. Pleistocene mammals have been preserved, trapped in mud, at a salt lick at Big Bone Lick in Boone County, northern Kentucky. Salt was obtained by early pioneers by boiling down water from salt springs, and it was a major item of trade for Native Americans and pioneers. The locations of salt springs were considered of strategic importance.