(b) Pyrope
(‘Cape-Ruby’)
Often quite ruby-red in colour ([Plate XXIX], Fig. 6), this variety is probably the most popular of the garnets. It is strictly a magnesium-aluminium garnet corresponding to the formula Mg3Al2(SiO4)3, but usually contains some ferrous oxide and thus approaches almandine. Both are included among the precious garnets. Its name is derived from πυρωπός, fire-like, in obvious allusion to its characteristic colour.
Although at its best pyrope closely resembles ruby, its appearance is often marred by a tinge of yellow which decidedly detracts from its value. Pyrope generally passes as a variety of ruby, and under such names as ‘Cape-ruby,’ ‘Arizona-ruby,’ depending on the origin of the stones, commands a brisk sale. The specific gravity varies upwards from 3·70, depending upon the percentage amount of iron present, and similarly the refractive index varies upwards from 1·740; in the higher values pyrope merges into almandine. Its hardness is slightly greater than that of quartz, and may be expressed on Mohs’s scale by the symbol 7¼.
An enormous quantity of small red stones, mostly with a slight tinge of yellow, have been brought to light at Teplitz, Aussig, and other spots in the Bohemian Mittelgebirge, and a considerable industry in cutting and marting them has grown up at Bilin. Fine ruby-red stones accompany diamond in the ‘blue ground’ of the mines at Kimberley and also at the Premier mine in the Transvaal. Similar stones are also found in Arizona and Colorado in the United States, and in Australia, Rhodesia, and elsewhere.
Although commonly quite small in size, pyrope has occasionally attained to considerable size. According to De Boodt the Kaiser Rudolph II had one in his possession valued at 45,000 thalers (about £6750). The Imperial Treasury at Vienna contains a stone as large as a hen’s egg. Another about the size of a pigeon’s egg is in the famous Green Vaults at Dresden, and the King of Saxony has one, weighing 468½ carats, set in an Order of the Golden Fleece.
(c) Rhodolite
This charming pale-violet variety was found at Cowee Creek and at Mason’s Branch, Macon County, North Carolina, U.S.A., but in too limited amount to assume the position in jewellery it might otherwise have expected. In composition it lies between pyrope and almandine, and may be supposed to contain a proportion of two molecules of the former to one of the latter. Its specific gravity is 3·84, refractive index 1·760, and hardness 7¼. It exhibits in the spectroscope the absorption-bands characteristic of almandine.
(d) Almandine
(Carbuncle)