Fluorite comes in a variety of natural colours and crystal formations and glows under ultraviolet light (the word 'fluorescence' comes from the same etymological source). In its pure form, calcium fluoride, it is a colourless combination of the elements calcium and fluorine, but gains its colour from trace elements that infiltrate or replace calcium within its crystal structure during its formation. Although fluorite crystals polish well and can achieve a high level of lustre, the mineral is very soft (4 on MOHS hardness scale) so it is unsuitable for use in rings and must be handled and stored carefully if used in other forms of jewellery. Most crystals of the mineral are too coarse for decorative purposes but have been mined under the name fluorspar for a variety of commercial and industrial purposes. These include the production of hydrofluoric acid, smelting metal alloys, producing glazes and ceramic finishes and use in medical and dental products. An existing label for this specimen indicates that its origin or collection-point was 'probably USA.' Fluorspar, the form of fluorite used commercially and industrially, was mined in significant quantities in the counties of Hardin and Pope in South-Eastern Illinois throughout the Nineteenth and Twentieth Centuries. Fluorite was made Illinois' state mineral in recognition of its contribution to the state's identity and economy. The specimens are significant as examples of surveying activity undertaken to assess and direct the development of the mineral resource industries, as well as the movement to expand human knowledge of earth sciences such as mineralogy and geology in the nineteenth century.The specimen is a piece of purple shaded fluorite (also known as fluorspar), the mineral form of calcium fluoride. The unpolished specimen presents a dark purple interior with a substantial dark grey crust representing the matrix from which the specimen was obtained. Existing label: Flourite / (purple) / probably / USA / BB /burke museum, beechworth, geological, geological specimen, fluorite, flourite, calcium fluoride, hydrofluoric acid, jewellery, indigo shire, north-east victoria, mining, illinois, usa, united states, fluorine, gemstones, purple stones