Fluorite is a mineral with a veritable rainbow of pastel colours. Known for its glassy lustre the most common colours for fluorite start from the purple, then blue, green, yellow, colourless, brown, pink, black and reddish orange. Only quartz rivals it for variety of shades. Differentiating similar coloured Amethyst and Fluorite crystals is often used as a test in mineralogical classes.
Most specimens of fluorite have a single colour, but a significant percentage of fluorites have multiple colours and the colours are arranged in bands or zones that correspond to the shapes of fluorite's crystals and just occasionally you will find a different colour crystal inside another.
The origin of the word fluorite comes from the use of fluorite as a flux in steel and aluminum processing. It was originally referred to as fluorospar by miners and is still called that today. As a child, I remember searching the ruins of copper and lead mines in the hills of northern England where good crystals could be collected from the spoil heaps.
Fluorite is also used as a source of fluorine for hydrofluoric acid and fluorinated water. As a gemstone it has good (if variable) cleavage although it is not very hard. Hence it is often found as polished nuggets as opposed to faceted gems. It can also be carved and clear crystals are even applied in optical lenses.