The refractive indices of all glasses at present available lie between 1.46 and 1 90, whereas transparent minerals are known having refractive indices lying considerably outside these limits; at least one of these, fluorite (calcium fluoride), is actually used by opticians in the construction of certain lenses, so that probably progress is to be looked for in a considerable widening of the limits of available optical materials; possibly such progress may lie in the direction of the artificial production of large mineral crystals.
The high level of fluorescence of fluorite from this classic area, adds an extra cachet other locations do not have.
Its newly designed optical system consists of 17 elements in 13 groups, including one fluorite and two UD lenses.
But the green fluorite on the right has more obvious cubes.
The fluoride in toothpastes is a chemical made from the mineral fluorite.