A selection of antique, hand-crafted Chinese jadeite buttons
|Category||mineral variety of pyroxene|
|Color||Semitransparent to opaque and often mottled, white, green, yellow to reddish orange, brown, gray, black, light purple or lavender.|
|Fracture||granular to splintery|
|Mohs Scale hardness||6.5 - 7|
|Refractive index||1.666 - 1.680 (+/- .008); spot reading is 1.66|
|Optical Properties||Double refractive with anomalous aggregate reaction |
|Birefringence||usually not detectable|
|Specific gravity||3.34 (+.06, -.09)|
Jadeite is one of the minerals recognized as the gemstone jade. Its color commonly ranges from white through pale apple green to deep green, but it can also be blue-green (like the famous, rediscovered "Olmec blue" variety), pink, lavender, and a host of other rare colors.
Jadeite is a pyroxene mineral with composition NaAlSi2O6. It is formed in metamorphic rocks under high pressure and relatively low temperature conditions. Albite (NaAlSi3O8) is a common mineral in the Earth's crust, with a specific gravity of about 2.6, much less than that of jadeite. With increasing pressure, albite breaks down to form the high-pressure assemblage of jadeite plus quartz. Minerals associated with jadeite include glaucophane, lawsonite, muscovite, aragonite, serpentine, and quartz.
Rocks that consist almost entirely of jadeite are called jadeitite. In all well-documented occurrences, jadeitite appears to have formed from subduction zone fluids in association with serpentinite (Sorensen et al. 2006). Jadeitite is resistant to weathering, and boulders of jadeitite released from the serpentine-rich environments in which they formed are found in a variety of environments.
Currently, the best-known sources of gem-quality jadeite are California, Myanmar (Burma), New Zealand, and (more recently) Guatemala. Other localities of jadeite include Kazakhstan, Russia, British Columbia, Alaska, and Turkestan.
Jadeite is composed of monoclinic crystals. Their colors are largely affected by the presence of trace elements, such as chromium and iron. The crystals can be anywhere from entirely solid through opaque to almost clear. Variations in color and translucence are often found even within a single specimen.
This mineral has a Mohs hardness of about 6.5 to 7.0 depending on its composition. It is dense, with a specific gravity of about 3.4. Jadeitite forms solid solutions with other pyroxene endmembers such as augite and diopside (calcium and magnesium-rich endmembers), aegirine (sodium and iron-rich endmember), and kosmochlor (sodium and chromium-rich endmember). Pyroxenes rich in both the jadeite and augite endmembers are known as omphacite.
Jadeite from the Motagua Valley, Guatemala, is the stone used by the Olmec, Maya peoples, and indigenous peoples of Costa Rica. Typically, the colors of jadeite most valued are the intensely green, translucent varieties, though traditionally white has been considered the most valuable of the jades by the Chinese, known for their carefully crafted jade pieces.
Currently, the most highly valued variety of jadeite is known as "Imperial Green" jade, characterized by an emerald green color and a high level of translucence. It the most expensive gem in the world, carat-by-carat, costing more than diamonds. Olmec blue jade, characterized by its deep blue-green, translucent hue with white flecking, is also becoming more highly valued because of its unique beauty and historical use by the Mesoamerican Olmec and the peoples of Costa Rica. The Olmec blue variety, however, was only recently rediscovered and is being minimally exploited by native Guatemalans. It is thus difficult to obtain and too rare and little-known to have attained great value as a gemstone.
When purchasing jade, quality is determined by the degree of translucence, cleanness of color, and purity of color. Occasionally, other minerals like serpentine or quartz are sold as jade but the difference can be determined by cleavage and hardness.
All links retrieved April 26, 2014.
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