Gems - Jade
( Originally Published 1919 )
THOUGH not usually accounted precious among European nations or in Western civilization in general, jade was held in extraordinary esteem by primitive man, and was fashioned by him into ornaments and utensils, often of considerable beauty, and even at the present day it ranks among the Chinese and Japanese peoples above all precious stones ; indeed, the Chinese word Yu and the Japanese words Giyuku or Tama signify both jade and precious stones in general. According to the Chinese, jade is the prototype of all gems, and unites in itself the five cardinal virtues-fin, charity ; Gi, modesty ; Yu, courage ; Ketsu, justice ; and Chi, wisdom. When powdered and mixed with water, it is supposed to be a powerful remedy for all kinds of internal disorders, to strengthen the frame and prevent fatigue, to prolong life, and, if taken in sufficient quantity just before death, to prevent decomposition.
Jade is a general term that includes properly two distinct mineral species, nephrite or greenstone, and jadeite, which are very similar in appearance, both being fibrous and tough in texture, and more or less greenish in ,colour ; but it is also applied to other species such as saussurite, californite, bowenite, and plasma, which have somewhat similar characters. The word jade is a corruption of the Spanish pietra di hijada, kidney-stone, in allusion to its supposed efficacy in diseases of that organ.
Nephrite or greenstone (Plate XXIX, Fig. 16) is the commoner of the two jades. It is closely allied to the mineral hornblende, a silicate of magnesium, iron, and calcium corresponding to the formula Ca(Mg,Fe)3(SiO3)4, the magnesia being replaceable by ferrous oxide. Microscopic examination shows that the structure consists of innumerable independent fibres foliated or matted together, the former character giving rise to a slaty and the latter to a horny appearance in the stone as seen by the unaided eye. The colour varies from grey to leaf- and dark-green, the tint deepening as the relative amount of iron in the composition increases, and brown tints result from the oxidation of the iron along cracks in the stone. The hardness is 6i on Mob's scale ; nephrite is therefore about as hard as ordinary glass and softer than quartz. When polished, it always acquires a greasy lustre. The specific gravity ranges from 2.9 to 3.1. The least and greatest of the principal refractive indices are 1.606 and 1.632 respectively, the double refraction being biaxial and negative ; the coloured fibres also display dichroism. All these differential effects are, however, masked in the stone because of the irregularity of the aggregation. Nephrite is fusible before the blowpipe, but only with difficulty. Its name is derived from the Greek word veopos, kidney, the allusion being the same as for jade.
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 Jordansmuhl, 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(SiO3)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.
A few words may be said about the other jade-like minerals. Saussurite, which is named after H. B. de Saussure, has resulted from the decomposition of a felspar, and is nearly akin to the mineral zoisite. It has the customary toughness of structure, and is greenish grey to white in colour. Its specific gravity is about 3.2, and hardness 6 to 7 on Mohs's scale. It occurs near Lake Geneva. Bowenite is a green serpentine (p. 289) which is found at Smithfield, Rhode Island, U.S.A., and in New Zealand and Afghanistan. Californite and plasma are compact varieties of idocrase (p. 275) and chalcedony (p. 247) respectively. Verdite is a stone of rich green colour which is found in the form of large boulders in the North Kaap River, South Africa ; it is composed of green mica (fuchsite) and some clayey matter.
Jade has of recent years been imitated in glass, but the latter is recognizable by its vitreous lustre and inferior hardness, and sooner or later by its frangibility.