In blue tourmaline and in iolite - stones sometimes mistaken for sapphire - the dichroism is much more distinct.
These reactions are of special interest, for they culminate in the production of artificial ruby and sapphire (see Gems, Artificial).
The sapphire is found in all the states, principally in the neighbourhood of Beechworth, Victoria.
African locality must be mentioned.; considerable finds were reported in 1905 and 1906 from gravels at Somabula near Gwelo in Rhodesia where the diamond is associated with chrysoberyl, corundum (both sapphire and ruby), topaz, garnet, ilmenite, staurolite, rutile, with pebbles of quartz, granite, vIII.
Supported on their heads is something like a crystalline firmament, above which is a form like a sapphire throne (cf.
Under artificial illumination many sapphires appear dark and inky, whilst in some cases the blue changes to a violet, so that the sapphire seems to be transformed to an amethyst.
The sapphire occurs also in Europe, being found in the Iserweise of Bohemia and in the basalt of the Rhine valley and of Le-Puy-en-Velay in France, but the European stones have no interest as gems.
The rolled crystals of sapphire occur, with garnet and other minerals, in glacial deposits, and have probably been derived from dykes of igneous rocks, like andesite and lamprophyre.
Purple corundum, or sapphire of amethystine tint, is called Oriental amethyst, but this expression is often applied by jewellers to fine examples of the ordinary amethystine quartz, even when not derived from Eastern sources.
As the sapphire crystallizes in the hexagonal system it is dichroic, but in pale stones this character may not be well marked.