55. _The ORIENTAL AMETHYST is an extremely rare gem, usually of purple colour, apparently formed by an union of the colouring matter of the sapphire and the ruby_. This stone, if heated, loses its colour, and becomes transparent. After this process its brilliancy is such that it is scarcely distinguishable from the diamond; and, in jeweller’s work, it is occasionally substituted for that gem. The common amethyst (79), or that which is chiefly seen, is nothing more than a violet─coloured rock crystal (78). 56. _The ORIENTAL TOPAZ and EMERALD are each varieties of the oriental ruby, the former straw─coloured and the latter green_. This kind of emerald is imported from Pegu, and some other parts of the East Indies, and is an extremely rare gem. 57. _The SPINEL and BALAIS RUBY are two kinds of precious stones, which differ from each other principally in colour, the former being of a carmine, and the latter a cochineal red._ _They vary from the oriental ruby (54) in being less hard; in the primitive form of their crystals being regular octohedrons (Pl. II, Fig. 5), and in their not being much more than 3 times heavier than water._ Although these two kinds of rubies are inferior, both in lustre and colour, to the oriental ruby; yet, when they exceed a certain size, they are much esteemed. A spinel that weighs more than four carats is valued at half as much as a diamond of the same weight, and is not unfrequently imposed upon ignorant purchasers for the oriental species. It is easily wrought, takes a high polish, and is certainly a beautiful gem. Being too expensive for necklaces, it is usually set in rings and brooches, surrounded by brilliants. The spinel ruby is found amongst sand, in one of the rivers of Ceylon, which flows from the high mountains, towards the middle of the island. It is also found in Brazil; and in Hungary, Bohemia, and Silesia. The Balais ruby is so named from Balacchan, the Indian appellation of Pegu, from which country it is chiefly imported. 58. _EMERY is a very hard opaque mineral, of blackish or bluish grey colour, which is chiefly found in shapeless masses, and mixed with other minerals. It is about four times as heavy as water._ The best emery is brought from the Levant, and chiefly from Naxos, and other islands of the Grecian Archipelago, where it occurs abundantly, in large, loose masses, at the foot of primitive mountains. It is also found in some parts of Spain; and is obtained from a few of the iron mines in our own country.