Ed. Note: The Stone of Heaven is one of the most revered natural substances in the world, such has been the case for centuries, particularly in Asia. What other mineral would make a Chinese emperor offer fifteen cities for a jade carving that he could hold in the palm of his hand or make Montezuma smile when he heard that the Spaniard Cortez was interested only in gold, since Montezuma's most precious possession was jade.
Since Neolithic times, no other mineral has been so venerated, nor so often intertwined with the dead to accompany them into the afterlife. In this life, to the Chinese, jade embodies the five cardinal virtues of life: charity, modesty, courage, justice, and wisdom. But China and Asia have not had a monopoly on jade; jade art and tools have been found in the Maori, Olmec, Aztec, and Mayan cultures, and among the NW American Coast Indians and Eskimos.
The English word jade has a circuitous derivation. It started with the Spanish expression "piedra de hijada", meaning the "stone of the loins", because it was claimed that this stone could cure diseases of the kidneys. This gave rise to the word nephrite, from the Greek word for kidneys: nephros. The French equivalent l'ejade eventually evolved into le jade, and its English translation, jade.
Jade is actually two minerals: nephrite and jadeite.
Nephrite is the ancient stone, a Calcium magnesium silicate: Ca2 Mg5 Si8 O22 (OH)2. Jadeite is the upstart of the two, having been discovered only 200 years ago, it is a sodium aluminum silicate: Na A1 Si2 O8. Both are insoluble in acids.
Nephrite is a tough, compact variety of tremolite and actinolite (amphiboles) with a specific gravity of 3.0 to 3.3, and a hardness ranging from 5 to 6 on the Mohs Hardness Scale. It is considered to be the world's toughest stone. Although it is not as hard as jadeite, it is much harder to break than its cousin. The reason for this is the filament-like crystalline structure of the mineral. When polished, nephrite has a soapy or oily luster. It is commonly referred to as "mutton-fat" jade, because of the marbled appearance that resembles animal fat. Nephrite is normally associated with serpentine, hornblende gneiss, and schist.
Jadeite is a hard, brittle mineral with a 3.3 to 3.5 specific gravity and a hardness of 6.5 to 7. It is pyroxenes, whose crystals are shorter and granular, and are more closely interlocked, as in a mosaic. Although it is harder than nephrite it fractures more easily. When polished, jadeite is vitreous or glassy. It is commonly found in association with albite feldspar, nepheline, and quartzite and is surrounded by serpentine.
Pure jade is white or transparent; the transparent variety is very rare. All other colorations of the stone owe to the addition of other elements. Although the five traditional colors of Chinese jade are red, black, white, yellow and green, jade can be found in all colors of the rainbow. Both nephrite and jadeite may be white or transparent or other colors. However, the vitreous apple and emerald green versions are almost assuredly jadeite. The milky silky or "mutton-fat" appearance is a clue that nephrite is the mineral inside. In general, the bold colors are never seen in nephrite, they are reserved for jadeite.
Jadeite and nephrite are minerals formed in a metamorphic environment associated with high pressure and a low temperature. While there are as many as seven hypotheses to explain the formation of the jade minerals, the most plausible is that they form under anomalously high water pressures on the lower plate of a low-angle thrust fault. In these circumstances, the fluid pressures may exceed the pressure of the rock overburden.
Such conditions may occur at the margins of the earth's plates, such as in the Alps, California, the northwest North American coast, and the Asian part of the Pacific Rim.
For twenty centuries, the main source of jade was the nephrite from China, found primarily as cobbles and boulders in the rivers and creeks. The river stones have a tough oxidized rind, making them not easily distinguishable from other stones. The Khotan and Yarkand regions, once the prime providers, are reportedly mined out of nephrite now, and nephrite boulders are only occasionally encountered.
In 1784, jadeite was discovered in northern Burma. Originally, it was also in the form of river cobbles and boulders. However, eventually the mother lode was found and mined. Although Burmese jade is not a large part of the international jade market because of political conditions there, these mines are still in operation. Jadeite was also located in China's Yunnan Province. Pre-Columbian implements and works of art in jadeite are thought to have originated in Guatemala.
Around the world, other sources of nephrite are: Lake Baikal, Russia; New Zealand; Switzerland; Zaire; Jordanow Slaski, Poland; British Columbia, Canada; Kotzebue, Alaska; Lander, Wyoming; and San Benito, California. Northern British Columbia now has the world's largest active nephrite mine near Dease Lake. About 300 tons are exported to Asia annually, and about 7 tons are used in North America for carvings and jewelry. Jadeite comes from Japan, western California, the Celebes, New Guinea, and Guatemala.
Jade does not have any other use in the modern world, except as a precious mineral and carving medium. In ancient times, it was also used to make household implements and weapons.
In the old days in Asia, jade was mined by building a charcoal fire near the mineral vein. At night, when the temperature dropped, the stone in the vein would crack. Workers would then drive stakes into the cracks to keep it open. Holes were drilled into the cracks, which were then filled with water so the freezing water would further expand the crack, eventually breaking a block free.
Modern methods are not entirely different. Drilling and blasting, along with heavy machinery, are used to remove the overburden of soil and rock. In British Columbia, large blocks and slabs are then removed from the mountain by drilling (2-inch-diam. holes) and hydraulic splitters. Hydraulic splitters are the mechanized versions of feathers and wedges. The low-quality nephrite is then separated from the high-quality with a 72-inch diameter saw. In general, the larger blocks are 5 to 10 tons, but the largest for a special carving was 25 tons. Cobbles and boulders are still used when found, but they are a minute proportion of the yield compared to years past
Jade is too hard to carve with conventional stone carving tools such as hammer and chisels. It is worked by grinding or abrading the stone away. From ancient times to only a few decades ago, jade was shaped by using hand-dipped quartz abrasives, along with hand tools, foot treadle machines, and bow drills. Presently, cutting and shaping of the stone is accomplished with diamond saws, drills, and grinding wheels.
Although tungsten carbide tools can be used with jade, the most cost effective are diamond tools. Diamonds can be used on all of the tools described, including the tiny bits that fit on the Foredom machine. The diamond sintered points with seven different grits can get into the smallest nooks and crannies. Sanding is normally accomplished with diamond compound that can be obtained in a lapidary shop. Deborah Wilson's secret polishing compound recipe contains diamond powder, vaseline, and lipstick (for tracking where you have polished). A water bath is used during grinding and polishing. The diamond polishing compound however, is only used dry.
When selecting jade, it is best to have two sawn sides to view. Early October is the best time of the year to obtain good pieces of the stone, because the best pieces of jade are still available soon after the summer quarrying season. White streaks in the otherwise green stone can be softer zones that may not work consistently with the rest of the stone.
Some of the inclusions that may be harder than the rest of the stone are blue-gray streaks, garnets, and flecks of chromite. Chromite inclusions in the finished piece have appeal to North Americans, but not the Chinese, who prefer pure colors.
Because jade contains silica in both minerals and nephrite is comprised of actinolite and tremolite, it is important to maintain a constant stream of water on the stone during grinding and to wear a respirator with very fine dust filters. And don't forget about eye protection.
Thanks to artist Deborah Wilson of Vernon, British Columbia for sharing her jade carving experiences and thanks also to quarry operator and jade merchant Kirk Makepeace of Jade West in White Rock, British Columbia for information on quarrying and availability of jade.