One of the most highly collected and prized specimens in the mineral realm is fluorite from southern Illinois.
Not only with a variety of colors - clear, yellow, white, blue and the most familiar purple, fluorite also can have many colors in one specimen, along with phantoms, windows, barite balls, marcasite, pyrite and some incredible zoning patterns.
Illinois fluorite is exceptional in that it forms cubes with cleavage planes that will cleave cleanly and precisely. This can create fluorite 'diamonds' that are amazing and very desirable to collect.
Fluorite can grow a smooth perfect cube naturally, as well as 'hopper' type cubes - which grow in an outer square and then fill in with smaller cubes. Fluorite is not has hard as quartz, however, and the cubes are sensitive to temperature change. Internal stresses within the cubes may change with age or with temperature fluctuations, and tunnels, windows and phantoms may appear and disappear over time. Fluorite provides an endless fascination.
Want to learn more about southern Illinois Fluorite? Check out the article on Terra Harmonia, Earthinsync's blog, at Illinois Fluorite-home grown 'diamonds'