JADE
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—_Jin_, 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}(SiO_{3})_{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 6½ on
Mohs’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 νεφρός, 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 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.
• • • • •
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 6½ 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.