Loose Gemstones | Gem Art | Gem Stone Information



	ANDALUSITE.	109

	Greenland, Iceland, the Faroe Islands, also Poonah, and Ahmed-nuggar in India yield fine crystals. It also occurs in many Swedish, Tyrolese, and Transylvanian localities. Apophyllite is nearly related to the zeolites, and is a hydrated silicate of lime and potash, with a little fluorine. Its percentage composition is represented by the following numbers— Andalusite. It is seldom that the mineral andulusite occurs in a perfectly transparent condition fit for cutting as a gem. Its colour is then of a somewhat reddish hue or pale amber brown, or light bottle green. But its beauty and interest mainly depend upon its conspicuous dichroism. Cut specimens often appear of a greenish hue, except in some of the end facets where a fine brownish red occurs.* There thus arises a marked resemblance to alexandrite, which, however, is not only a much more valuable stone, but is also heavier and harder. It may also be confused with certain tourmalines of similar hue, but its specific gravity is rather greater, while the pyro-electric character of tourmaline affords a means of distinguishing the two stones. Andalusite, which crystallises in the rhombic system, occurs in prismatically developed forms of which the section is nearly square. Its hardness is at least 7-1/4 and its specific gravity close to 3'18. Transparent specimens occur in some abundance in the Minas Novas district of Brazil, but are also found in certain gem gravels of Ceylon, where the stone is mistaken for tourmaline. A step-cut shape with few and rather large facets generally suits andalusite. The composition of andalusite is identical with that of cyanite * Fig. 7. Frontispiece.