Jadeite

This article is about the mineral. For other uses, see Jadeite (disambiguation).

Jadeite
Jadeite
General
Category	Pyroxene group
Chemical formula	NaAlSi2O6 or Na(Al,Fe3+)Si2O6
Identification
Color	Apple-green, emerald-green, bluish green, leek-green, greenish white, white, may show green spots, rarely blue or violet; colorless in thin section
Crystal habit	Commonly massive, or fibrous, granular — prismatic crystals rare
Crystal system	Monoclinic prismatic
Twinning	Single and lamellar twinning on [100] and [001]
Cleavage	Good on [110]
Fracture	Splintery
Mohs scale hardness	6 - 7
Luster	Subvitreous, pearly on cleavages
Streak	White
Diaphaneity	Translucent
Specific gravity	3.24 to 3.43
Polish luster	vitreous to greasy[1]
Optical properties	Biaxial (+)
Refractive index	nα = 1.654 - 1.673 nβ = 1.659 - 1.679 nγ = 1.667 - 1.693
Birefringence	δ = 0.013 - 0.020
Dispersion	r > v; moderate to strong.
Ultraviolet fluorescence	Dark colors are generally inert. Light green - inert to weak white in long wave, generally inert in short wave; light yellow - inert to weak green in long wave, generally inert in short wave; white - inert to weak in long wave, generally inert in short wave; light purple - inert to weak white or weak brownish red in long wave, generally inert in short wave; some dyed lavender colors - moderate to strong orange in long wave, weaker in short wave [1]
References	[2][3][4]

Jadeite is a pyroxene mineral with composition NaAlSi₂O₆. It is monoclinic. It has a Mohs hardness of about 6.5 to 7.0 depending on the composition. The mineral is dense, with a specific gravity of about 3.4. Jadeite forms solid solutions with other pyroxene endmembers such as augite and diopside (CaMg-rich endmembers), aegirine (NaFe endmember), and kosmochlor (NaCr endmember). Pyroxenes rich in both the jadeite and augite endmembers are known as omphacite.

A selection of antique, hand-crafted Chinese jadeite buttons

The name Jadeite is derived (via French: l'ejade and Latin: ilia ^[5]) from the Spanish phrase "piedra de ijada" which means "stone of the side." It was believed to cure kidney stones if it was rubbed against the side of the afflicted person's body. The Latin version of the name, lapis nephriticus, is the origin of the term nephrite, which is also a variety of jade.

Jadeite is formed in metamorphic rocks under high pressure and relatively low temperature conditions. Albite (NaAlSi₃O₈) is a common mineral of the Earth's crust, and it has 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.^[6] 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.

Jadeite's color commonly ranges from white through pale apple green to deep jade green but can also be blue-green (like the recently rediscovered "Olmec Blue" jade), pink, lavender, and a multitude of other rare colors. Chloromelanite is a very dark green to black variety.^[7] Color is largely affected by the presence of trace elements such as chromium and iron. Its translucence can be anywhere from entirely solid through opaque to almost clear. Variations in color and translucence are often found even within a single specimen. Currently, the best known sources of gem quality jadeite are California, Myanmar, New Zealand and more recently Guatemala; other localities of jadeite include Kazakhstan, Russia, British Columbia, Alaska, Italy and Turkestan.

Over 100 axe heads made from jadeite quarried in northern Italy in the Neolithic era have been found across the British Isles.^{[8] [9]}Because of the difficulty of working this material, all the axe heads of this type found are thought to have been non-utilitarian and to have represented some form of currency or be the products of gift exchange.^[10]

Jade

Jadeite rock with finished jade Buddha statue, from China, American Museum of Natural History, NewYork City

Jadeite is one of the minerals recognized as the gemstone jade. The other is nephrite. Jadeite from the Motagua Valley, Guatemala, was used by the Olmec and Maya peoples, as well as the indigenous peoples of Costa Rica. Typically, the most highly valued colors of jadeite are the most 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. Other colors, like "Olmec blue" jade, which is characterized by its deep blue-green, translucent hue with white flecking, are also becoming more highly valued because of its unique beauty and historical use by the Mesoamerican Olmec and also in Costa Rica;^[11] however, this variety was only recently rediscovered and is only being minimally exploited by native Guatemalans. It is thus difficult to obtain and as yet 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.

Polished Neolithic ax - Museum of Toulouse

See also

• Clinopyroxene thermobarometry
• Costa Rican jade tradition
• Jade use in Mesoamerica

References

1. ^ ^{a b} (Gia), Gemological. Gem Reference Guide. City: Gemological Institute of America (GIA), 1988. ISBN 0-87311-019-6
2. ^ http://rruff.geo.arizona.edu/doclib/hom/jadeite.pdf Handbook of Mineralogy
3. ^ http://www.mindat.org/min-2062.html Mindat
4. ^ http://webmineral.com/data/Jadeite.shtml Webmineral data
5. ^ http://www.etymonline.com/index.php?term=jade
6. ^ Sorena Sorensen, George E. Harlow, and Douglas Rumble, The origin of jadeitite-forming subduction-zone fluids: CL-guided SIMS oxygen-isotope and trace-element evidence. American Mineralogist, v. 91, pp. 979-996 (2006)
7. ^ http://www.mindat.org/min-1023.html Mindat
8. ^ "Jadeite axe-head". British Museum. http://www.britishmuseum.org/explore/highlights/highlight_objects/pe_prb/j/jadeite_axe-head.aspx. Retrieved 21 November 2009. 
9. ^ "Jadeite axe". Wiltshire Heritage Museum. http://www.wiltshireheritage.org.uk/galleries/index.php?Action=4&obID=116&prevID=80&oprevID=12. Retrieved 31 October 2011. 
10. ^ Barker, Graeme (1999). Companion encyclopedia of archaeology. New York: Routledge. pp. 378. ISBN 0-415-21329-0. 
11. ^ Easby, Elizabeth Kennedy. Pre-Columbian Jade from Costa Rica. (1968). André Emmerich Inc., New York