Dichroite is sometimes known under the mineralogical names of cordierite and iolite, and commercially as saphir d’eau, or water sapphire. This stone is remarkable for pleichroism, sometimes showing three different colors in as many directions, and when properly cut has often the star formation of the corundum star-stones.

Water sapphire, as the blue specimens are called, is 7 to 7.5 in hardness, specific gravity 2.56 to 2.67, transparent to translucent, and frequently full of flaws. It is partially decomposed by acids, melts with difficulty before the blow-pipe, is vitreous to greasy in lustre, and is composed of:

Besides the saphir d’eau, which is blue, dichroite occurs colorless, bluish-white, yellowish-white, yellowish-gray to yellowish-brown, indigo to blackish-blue, and violet. This mineral is found in Ceylon, Spain, Norway, Sweden, Tuscany, Greenland, and Bavaria. Sapphire is harder and much heavier than dichroite.