This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1903 edition. Excerpt: ...the high refractive power and hence play of colors of the latter. The stones are sometimes called "Matura diamonds," because of their abundance at Matura in the island of Ceylon. The colorless, or smoky zircons, are often known as "jargons" or "jargoons," a name said to have been given in allusion to the fact that though they resembled the diamond in luster they had really much less value. Besides zircons of this sort there are those known in jewelry as "hyacinth" or "jacinth," which are transparent zircons of a brownish, red-orange color. A stone of a nearly similar color is furnished by the essonite variety of garnet, and this is also often known as hyacinth. The high specific gravity of zircon above referred to is more than four times the weight of water, determinations giving results varying between 4.2 and 4.86. Zircon is thus the heaviest of gems, and will sink at once in any of the ordinary heavy liquids. The hardness of zircon is between that of quartz and topaz, being 7 . Its index of refraction is high, being 1.92, or near to the diamond among gems, a fact which accounts for its brilliancy when cut. Before the blowpipe zircon is infusible. It is not acted upon by acids except in fine powder by sulphuric acid. In composition it is a silicate of zirconium, the percentages being silica 32.8, zirconia 67.2. It usually also contains a little iron oxide. It is not an uncommon mineral in rocks, occurring in crystals of microscopic size, and in crystalline rocks it sometimes occurs in large and abundant crystals. These are usually opaque and of no value for gem purposes, although they are mined to some extent at the present time for use in incandescent lights. Opaque zircon is found...