Friday, September 7, 2012

The Chemical Properties of Jadeite Jade

Jadeite Jade, small boulder
Photo Credit: Jadeite Jade
by Angela Magnotti Andrews

Jadeite jade, found in abundance primarily in Burma, Guatemala, and Japan, is the most highly prized form of jade in commercial jade markets. It is harder, denser, and more brilliantly colored that its fraternal twin, nephrite jade. Its scarcity and physical properties make one carat of top-quality rough jadeite worth far more than even one pound of the best rough nephrite.

Comprised primarily of single chains of silicon and oxygen atoms intruded by sodium and aluminum, jadeite jade is also the most popular choice for jewelry, as it forms in the highly favored emerald green color often referred to as "Imperial Jade" or "Emerald Jade." Imperial jade can also have a slightly bluish-green tone.

Chemically speaking, jadeite is classified as a pyroxene, which makes it a rock-forming silicate which contains sodium and aluminum which derives its various colors from intrusion of trace elements withing the crystal mesh structure. Trace amounts of chromium and possibly some iron are responsible for the brilliant greens while iron gives jadeite a yellow-to-yellowish-green tint. Lavender jadeite, another popular choice for jewelry, owes its coloring to either manganese or iron charge transfer.

In appearance, jadeite is granular and will be slightly dimpled once polished (due to undercutting). It is rare to see visible crystals in a piece of jadeite, though upon magnification its crystals appear as individual slender blades. Jadeite has a monoclinic structure with cleavage of 90 degrees and is void of water molecules (anhydrous).

Jadeite can vary widely in composition, sometimes grading into other pyroxene minerals. As long as a specimen of this nature maintains jadeite's gemological properties (Refractive Index of 1.660 - 1.680a +0.10b, spot 1.66; Specific Gravity of 3.34 + 0.11b; and Hardness of 6.5 - 7 on Mohs Scale), it can be labeled and sold as jadeite.
BIBLIOGRAPHY
1. "Jade (Jadeite, Nephrite)." University of Texas, Geology. Last updated August 20, 2009. http://www.geo.utexas.edu/courses/347k/redesign/gem_notes/jade/jade_main.htm.
2. Katz, Bob. "Jade." Exploring the Southwest Desert USA. Accessed September 5, 2012. http://www.desertusa.com/mag98/aug/papr/geo_jade.html.
3. Keverne, Roger, ed. Jade. New York: Lorenz Books, 1995.
4. Leaming, Stan and Hudson, Rick. Jade Fever: Hunting the Stone of Heaven. Surrey, BC: Heritage House Publishing Co. Ltd., 2005.
5. "Mesoamerican Jade." Authentic Maya. Last updated January 28, 2011. http://www.authenticmaya.com/Jade.htm.
6. "Mineral Jadeite, The." The Mineral & Gemstone Kingdom. Accessed September http://www.minerals.net/mineral/jadeite.aspx.

*Clip art courtesy of The Graphics Fairy


1 comment: