Fluorspar

Fluorspar (or, to use its mineral name, fluorite) is calcium fluoride (CaF2). While most commonly used to refer to the mineral when mined from the Earth’s crust, fluorspar also refers to the calcium fluoride produced as a by-product in various chemical processes, such as the production of phosphoric acid, refining petroleum or enriching uranium for fuel.Theoretically, pure fluorspar (51.1% calcium and 48.9% fluorine) is colorless, but in the earth, the many different impurities found in the mined mineral imbue it with a variety of wonderful colors, ranging from blue, green and purple, to pink, brown and black. Indeed, in the 19th century, much of the fluorite mined was used to make jewelry.
Times have changed, and while a minuscule amount of fluorspar still goes into ornaments, the vast majority serves very different purposes.