Gems Notes and Extracts Augusto Castellani, Mrs. John Brogden 1871

226 GEMS.The sapphire is also divided into two kinds, viz.,Eastern and Western.The Oriental sapphire is a clear corundum, which hasall the gradations of blue. It is found only in India,and especially in Ceylon.In hardness it is equal, if not inferior, to that ofthe red corundum.Its crystals, like those of other corundums, havethe primitive form of a dodecahedron with triangularfaces, but most frequently they are rounded.Its specific gravityis 4-01. It possesses doublerefraction in such a degree as to surpass every otherstone, not excepting the diamond.It takes its place amongst the translucent and transparentgems, and often its imperfect crystallizationgives it a milky opacity.Like the ruby, it iscomposed of alumina almostpureits colorization being due to oxide of iron. It is;remarkable how the same metallic oxide produces twosuch different colours in the same stone ;and, whilstremembering that the ruby darkens at the fire, and thesapphire tends to becoming colourless, we must attributethis diversity to the greater or less oxidation experiencedby the metal at different degrees of heat.The Oriental sapphire, to be considered beautiful,must have a clear blue colour, not too light, and ofperfect limpidity.It thus appears soft as velvet, and is so charmingthat it justifies the simile used by Dante to indicatethe clearness and vivacity of the air :