jadeite

n.
A rare, usually emerald to light green but sometimes white, auburn, buff, or violet mineral, NaAlSi₂O₆, used as a gem and for ornamental carvings. It is the tougher and more highly valued form of jade.

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The monoclinic sodium aluminum pyroxene, NaAlSi₂O₆. Free crystals are rare. Jadeite usually occurs as dense, felted masses of elongated blades or as fine-grained granular aggregates. It has a Mohs hardness of 6.5 and a density of 3.25–3.35. It has a vitreous or waxy luster, and is commonly green but may also be white, violet, or brown.

Jadeite is always found in metamorphic rocks. It is associated with serpentine at Tawmaw, Burma; Kotaki, Japan; and San Benito County, California. It occurs in metasedimentary rocks of the Franciscan group in California and in Celebes. It is found in Tibet; Yunan Province, China; and Guatemala.

Jadeite is the more cherished of the two jade minerals, because of the more intense colors it displays. It is best known in the lovely intense green color resembling that of emerald. See also Jade; Pyroxene.

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Na(Al,Fe)Si
Monoclinic -- prismatic

Environment

Little known in place, usually in waterworn boulders; freed by weathering from masses formed in serpentine by alteration of a soda-rich rock (nepheline and albite can be altered to jadeite).

Crystal description

Free (pocket) crystals are known only from California. Usually in distinctly granular masses of somewhat elongated blades, which give thin slices strength (but coarser and less tough than the finer-textured nephrite masses). Individual Mexican crystals, commonly associated with albite, are coarser (to ƈ in., 1-2 mm across), and less uniformly translucent than high-quality Myanmar material. Polished slabs sometimes show a silky luster from parallel cleavage cracks.

Physical properties

Emerald to light green, white, violet, lilac, malachite green. (Boulder surfaces weather to yellow, orange, or red-brown, and skins of this hue are often left on Chinese artifacts). Luster glassy to silky; hardness 6Ɖ-7; specific gravity 3.3-3.5; fracture difficult, splintery; cleavage prismatic. Translucent to opaque.

Composition

Sodium aluminum silicate (15.4% Na ₂ O, 25.2% Al ₂ O ₃ , 59.4% SiO ₂ ; some varieties, particularly that of Mexican artifacts, quite high in CaO and mixed with albite).

Tests

Fuses easily to a bubbly white glass, with a yellow sodium flame coloration.

Distinguishing characteristics

Differs from far more common nephrite by its easy fusion and yellow flame coloration. Distinguished in worked objects by its gravity, which also separates it from idocrase and massive grossular. Hardness tests readily distinguish jade from soft-mineral (serpentine, agalmatolite, fluorite) carvings without any need for gravity tests, which can be complicated for large objects.

Occurrence

Until recent years jadeite has been something of a mystery mineral, but we now know of primary sources in Guatemala as well as several California occurrences of white or grayish jadeite. Boulders in which a few small freestanding crystals have been seen occur in San Benito Co., California, with additional finds in Clear Creek, between New Idria and Hernandez. All Mexican jadeite is in artifacts, from unknown sources. Little of the Guatemalan rough resembles the fine bluish Olmec or richly green Mayan material; the sources for these are yet undiscovered (probably gathered as stream boulders, so now unrecognized). "Chinese" jadeite is mostly found as boulders in streambeds in Myanmar and traded to the Chinese carving centers. Low-quality rough has been found in place at one locality in Japan.

Remarks

A valuable material for gem purposes (almost transparent emerald green stones are very valuable); the larger, less translucent and colorful masses are widely used for carvings in China. Color is often spotty, and sometimes present only as thin green seams in paler material with a spotty color pattern that can encourage a carver to excise detracting grains in favor of holes. Jadeite can be dyed and/or bleached, and buyers should observe caution, especially with violet jadeite.

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jadeite