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Jade

Jadeite - Nephrite


Jade is the name used to describe either of two hard, dense, usually green gemstones. The more highly prized of the two is Jadeite -- the other is Nephrite. Both jadestones take a high polish. Both have been carved into jewelry, ornaments, small sculptures and tools from the earliest recorded times.

JadeJadeite and nephrite differ in both crystalline structure and chemical composition. In both minerals, the microscopic crystals are tightly interlocked to form a compact aggregate. Jadeite is a silicate of sodium and aluminum and is classed as a pyroxene. Nephrite is a silicate of calcium and magnesium belonging to the amphibole group of minerals; it is usually called a form of Tremolite.

Both jadestone types may be white or colorless, but may occur as red, green, brown, purple, yellow or gray due to the presence of iron, chromium or manganese. There are also wide variations of translucency in both minerals. The most highly prized variety is jadeite of an emerald-green hue. The two different types of jadestones, when worked and polished, can be distinguished by their appearance. The luster of polished nephrite is oily; that of jadeite is glassy. Some colors are also specific to one mineral or the other. The popular emerald-green jewelry jades are usually jadeite. The main source of gem-quality jadeite is northern Myanmar (Burma). Nephrite occurrence is more geographically widespread, including North America.

Because both jadestones are hard, tough and keep a good edge, they were fashioned into tools by Neolithic peoples in many parts of the world. The best-known finds are from the lake dwellings of Switzerland, western France and China. When stone-based Neolithic cultures were succeeded by those bronze and iron, jade gradually lost its value in all but a few regions of the world.

Jade and jade carving are associated predominantly with the Chinese, who, from the Neolithic period, were carving jade into tools and simple cult objects in the form of flat donut-shaped disks. Nowhere else has jade been worked with such skill in such a long and unbroken tradition. For thousands of years, the Chinese carved only nephrite from within its own provinces. Not until the 18th century, did they begin to work jadeite when large quantities began entering the country from Myanmar.

The Aztecs, Mayas and other Native American peoples of Mexico and Central America carved jadeite for use as ornaments, amulets and badges of rank. Nearly all of these Meso-American jades are of various shades of green, with emerald green the most highly prized color among the Aztecs. The appreciation of jade died out in Meso-America after the Spanish conquest in the 16th century.

Several varieties of the mineral serpentine resemble nephrite and are sometimes sold as such, but they can be distinguished by their relative softness. Another deceptive practice is that of dyeing colorless pieces of jade green to simulate high-quality stone.

JADEITE
Chemistry
Crystal System
Hardness
 Na(Al,Fe)Si2O6
 Monoclinic
6.5 - 7.0
Cleavage
 Fracture
Specific Gravity
 Prismatic
Difficult, splintery
3.3 - 3.5
Color, Transparency
& Luster
 VARIETIES 
- Color colorless, white, light green, white, red-brown, yellow-brown, violet, lilac
- Streak translucent to opaque
- Luster glassy


NEPHRITE
Chemistry
Crystal System
Hardness
 Ca2(Mg,Fe)Si8O22(OH2)
 Monoclinic
5.0 - 6.0
Cleavage
 Fracture
Specific Gravity
 Prismatic
Subconchoidal to Uneven
3.0- 3.3
Color, Transparency
& Luster
 VARIETIES 
- Color colorless, white, light green, white, red-brown, yellow-brown, violet, lilac
- Streak translucent to opaque
- Luster oily to silky

-- Bob Katz


 


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