Many of the prehistoric implements found in Mexico and in the Swiss Lake Habitations are composed of nephrite, but it is uncertain where the mineral was obtained. Much of the material used by the Chinese at the present time comes from spots near the southern boundary of Eastern Turkestan, especially in the valleys of the rivers Karakash and Yarkand in the Kwen Lun range of mountains; it is also found farther north at the river Kashgar. It occurs in various provinces of China, namely, Shensi, Kwei Chau, Kwang Tung, Yunnan, and Manchuria. Gigantic waterworn boulders have been found in the Government of Irkutsk, near Lake Baikal, in eastern Siberia, the first discovery being made in the bed of the Onot stream by the explorer and prospector J. P. Alibert, in 1850. A large boulder of this kind, weighing over half a ton (1156 lb., or 524·5 kg.), is exhibited in the Mineral Gallery of the British Museum (Natural History). An enormous mass, weighing over 2 tons (4718 lb., or 2140 kg.), was discovered at Jordansmühl, Silesia, by Dr. G. F. Kunz, and is now in the magnificent collection of jade formed by Mr. Heber R. Bishop. Beautiful greenstone occurs in New Zealand, particularly in the Middle Island. The Maoris have long used it for various useful and ornamental purposes, the most common being indicated by their general name for the species, _punamu_, axe-stone; _kawakawa_ is the ordinary green variety, a fine section of which is shown on the wall of the Mineral Gallery of the British Museum (Natural History), while _inanga_, a grey variety, and _kahurangi_, a pale-green and translucent variety, are rare and highly prized. Jadeite (Plate XXIX, Fig. 18) is by far the rarer of the two jades, and is the choicest gem with the Chinese. In composition it is a silicate of sodium and aluminium with the formula NaAl(SiO_{3})_{2}, corresponding to the lithium mineral spodumene (p. 265). It has the same toughness and greasy lustre as nephrite, but is harder, being represented by the symbol 7 on Mohs’s scale, and thus only slightly, if at all, softer than quartz. The other characters are also higher; the specific gravity is about 3·34, and the least and greatest of the principal refractive indices are 1·66 and 1·68, the double refraction being biaxial and negative. The colour varies from white to almost an emerald green, the latter being especially prized, and often the green colour runs in streaks through the white. Jadeite fuses readily before the blowpipe to blebby glass, more easily than is the case with nephrite. The finest jadeite comes from the Mogaung district in Upper Burma, where it is found in boulders and also with albite in dykes in a dark-green serpentine. The export trade to China, which absorbs practically the whole of the output, is exceedingly valuable, and realizes nearly as much as the produce of the ruby mines. Jadeite is also found in the Shensi and Yunnan provinces of China, and in Tibet.