Sunday, March 3, 2013

Jade - An Extraordinary Gemstone

 This sample of jade shows the extreme deformation required to produce jade. Numerous fractures in the original rock allowed fluids to fill open spaces and replace the original basalt with dark green nephrite jade, while fractures were rehealed with white jade and finally, after things started to calm down, later fractures were filled with apple green jade veins before Mother Nature uplifted the Granite Mountains in Wyoming allowing erosion to free the jade over millions of years. Specimen from the Jay G. Sundberg collection.
Some extraordinary pressures, temperatures and chemistry are required to produce jade. The metamorphic fluids released by rocks at great depth are so caustic that they replace the original rocks and even replace quartz. As the fluids migrate out into the rock they are replacing at great depth in the earth's crust, they leave a aureole of alteration assemblages that can be used by a trained geologist and prospector to find hidden jade deposits that may now be exposed at the earth's surface following millions (even billions in some cases) of years of deformation, uplift of mountain ranges and erosion.  When prospecting in the Granite Mountains for gold and ruby, many alteration haloes were identified by geologist Dan Hausel, suggesting that either a jade deposit was hidden at shallow depth, or they jade had already been removed by Mother Nature's erosion.

Emerald green jade with quartz inclusions (Jay G. Sundberg collection).

Prismatic white quartz crystal preserved in dark green jade (Jay G. Sundberg collection).

 
Another sample of prismatic quartz preserved in jade. The original rock was likely a high magnesium basalt. The entire rock matrix of the former basalt was replaced by the nephrite jade while leaving the quartz crystal untouched (Jay G. Sundberg collection).
Hexagonal jade? This is a piece of prismatic quartz which was entirely
replaced by nephrite jade. Note the specimen exhibits a distinct hexagonal
crystal habit typical of quartz (but not of jade). Specimen found in the Tin Cup
district of the Granite Mountains (W. Dan Hausel collection).


Jade cabochon with feldspar (Jay G. Sundberg collection).
Pitted jade (Jay G. Sundberg collection).
Mirror of Jade with jade plant. This specimen from the Jay Sundberg collection has such a high polished reflective surface that it can be used to comb your hair.


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Thursday, October 29, 2009

Jade - how to find this extraordinary gemstone.

Jade is the gemologist's term for two different mineral species: nephrite and jadeite. These two minerals are nearly impossible to distinguish from one another without the aid of mineralogical and XRD (x-ray diffraction) tests.

Nephrite is categorized as an amphibole and consists of extremely dense and compact fibrous tremolite-actinolite; and jadeite is categorized as a pyroxene, and also forms dense and
compact material.

This map from the Wyoming Geological Survey is unfortunately misleading. The only place in the state where neprhite Jade has been identified is in the central part of the state in the granite Mountains and Crooks-Gap Green Mountain near Jeffrey City. Some of the other localities are questionable. For example, the author was unable to find any jade in the Seminoe Mountains during two years of field investigations (Hausel, 1993, 1994), and the occurrence along the southern edge of the Wind River Mountains (Prospect Mountains) was later examined and all the material reported as nephrite jade was amphibolite (Hausel, personal field notes).
Many rocks are mistaken for jade. Some of the more common include rounded, stream-worn or wind-polished cobbles of amphibolite (a dark metamorphic rock that resembles dense basalt), metadiabase (another dark metamorphic rock that also resembles basalt), epidotite (a dense pistachio green rock), quartzite (granular rock that can be white, dark gray, green or other colors) and serpentinite (dark green rock that can be scratched with a pocket knife). These rocks can be distinguished from jade by a couple of tests including simple field observations. For example, amphibolite and metadiabase have granular texture that is lacking in most jade (jade is smooth and massive without granular texture). A freshly broken surface of quartzite will sparkle in sunlight due to the reflection of light bouncing off individual quartz grains; and epidotite has a distinct pistachio green color (unlike jade). One of the more common rocks and minerals mistaken for jade is serpentinite (a rock formed mostly of serpentine). Jade is tough and hard, whereas serpentinite is relatively soft and can be scratched with a pocket knife. In addition, serpentinite will have pockets or zones of weak to moderate magnetism that can be detected by a geologist’s magnet. I’ve never seen a piece of magnetic jade, although some probably occurs.

I’ve seen serpentine sold to unsuspecting tourists as apple green jade. I even showed one rock shop owner that most of the material he was selling was serpentinite, but he refused to listen and continued to sell it as high-quality apple-green jade – and probably still does to this day.

When prospecting for jade, note that jade boulders will ring when struck by a hammer. They feel much heavier than ordinary rocks, and are much smoother and denser than other boulders. Some boulders and cobbles of jade are so smooth that it gives an impression the stone was polished in a rock tumbler. Jade feels slightly sticky when wet and prospectors will look for a “show point,” area where the green color shows through altered rinds that encrust much detrital jade.
Light green muttonfat jade from the Granite Mountains. Note the crystal is
hexagonal (6-sided) just like quartz. This jade replaced a former
quartz crystal leaving behind this rare pseudomorph).
Jade never shows external crystal structure except in rare cases where it pseudomorphs, or mimics the crystal habit of another mineral. I had heard about this phenomenon from a couple of rock hounds over the years, but never witnessed it until about 10 or 15 years ago when I found a pocket of hexagonal jade in the Granite Mountains (Wyoming) northeast of the Red Dwarf ruby deposit that had the same crystal habit as quartz.

Microscopically, jade will form a mass of matted, intricately interwoven fibers that produce an extremely tough gemstone resistant to fracturing. Mineral toughness is rarely considered in mineralogy books, but any discussion of jade always leads to a discussion of toughness. The toughness of a mineral is represented by its fracture strength (or ability to resist fracturing), which is about 30,000 psi for nephrite. In other words, it takes a lot of pressure to fracture a coherent piece of jade. Only carbonado, a black granular to compact industrial form of diamond, is tougher than jade; whereas gem-quality diamond is hard, but not all that tough. Gem diamond can scratch almost anything, but it can be smashed with a little effort with a blow from a hammer. It is the toughness of jade, combined with hardness that makes the gem carvable, durable and unique.
Look closely at this jade and you will see several individal jade crystals that are roughly hexagonal. These are also jade pseudomorphs after quartz. During the geological past, the jade slowly replaced the quartz one atom at a time without disturbing the original crystal habit of the quartz.

Jade ranges from opaque to translucent masses and has a vitreous to waxy luster and is reported in a variety of colors including black, white, and several shades of green. The green color is due to the presence of iron. When iron is absent, the mineral is practically colorless to cloudy white, resulting in a variety known as ‘muttonfat jade’. Other varieties of jade include translucent, emerald-green ‘imperial jade’; ‘apple-green’ jade, ‘olive-green’ jade, ‘leaf-green‘ jade, ‘black‘ jade, and ‘snowflake’ (mottled) jade. The greater commercial values are attached to the lighter green translucent varieties. Rare emerald green jade is colored by iron and trace amounts of chromium.

The extraordinary color of apple green jade.

The origin of nephrite jade was investigated in the 1960s. It is thought that nephrite formed by metasomatic alteration of amphibole during metamorphism. This means that hot fluids reacted with existing amphiboles and slowly replaced them by extracting some atoms and replacing those atoms with new atoms. In Wyoming, this happened when these rocks were buried under several miles of rock about 2 to 3 billion years ago. Blocks of amphibolite were disrupted and trapped in a molten granitic rock and portions of the amphibolite (xenoliths) were altered to jade by the hot granitic fluids. These reactive fluids not only produced jade, but they also altered the surrounding rocks to produce a group of minerals that included clinozoisite, zoisite, sericite and chlorite.

When found in outcrop, nephrite jade is associated with this distinct assemblage of minerals that form an alteration halo around jade. This halo consists of bleached leucocratic (white) granite-gneiss that is mottled pink and white, some secondary greenish clinozoisite, pink zoisite, pistachio green epidote, green chlorite and fine white mica. This alteration halo can be used as a guide to find hidden jade deposits. While exploring between some jade deposits north of Jeffrey City to the jasper deposits in the Tin Cup district to the west, I found more than a dozen such halos – a couple had exposed jade, others did not. The ones without jade, such as shown in the photo below, likely have hidden jade at shallow depth.

Characteristic wallrock alteration found with jade includes bleached white granite gneiss with pink zoisite, green chlorite and trace epidote. While searching north of Jeffrey City, I found more than a dozen areas with this characteristic alteration halo. Where found, this halo represents places where jade or hidden jade is likely to be found (with some digging). Below right– leaf-green jade fashioned into arrowheads.

The name jade comes from the time of the Spanish conquest of Central and South America where jade and jade carvings were prized as much as gold by the Aztecs. The Spanish used the name piedra de hijada, or stone of the side, because it was believed that jade cured kidney ailments when applied to the side of the body. The Spanish also called this stone kidney stone or piedros de los rinones, which translated into Latin as lapis nephriticus. The term nephrite anglicized the Latin term for jade. Nephrite has been known as ‘axe-stone’ because many nephrite stone artifacts have been found that were shaped into axe-heads due to its toughness. Although primary deposits of jade are important, much of the finest material comes from secondary alluvial deposits.

Some incredible pieces of jade have found their way to the jewelry industry. For example, one small jadeite ring sold for more than US$2.4 million: a 27-bead emerald green jadeite necklace sold in Hong Kong for US$9.3 million. In 1999, a 2-inch diameter (0.33-inch thick) jadeite bangle sold at a Christie's auction for US$2.6 million and a jadeite cabochon of 1.4-inches in length sold for US$1.74 million!


Black Jade from Wyoming
All of the jade found in Wyoming is nephrite, whereas much of the jade mined in the Orient is jadeite.

Translucent Jade Cabochon from Wyoming

For those interested in searching for jade in Wyoming, it is found primarily in the Granite Mountains and to the south at Crooks Gap-Green Mountain. It has been reported elsewhere in the state, but much of the material reported outside of the Granite Mountains has turned out to be serpentinite.

The best jade specimens found in Wyoming are peb­bles and boulders in alluvial fans and soil around Jeffrey City. Cobbles and boulders are found south of US Highway 287 (789) while jade (in place) is found in outcrops to the north of the highway in the Granite Mountains.


Another strange rock. A former igneous rock that was almost entirely
replaced by nephrite jade.
The jade localities are described in the following books:

Hausel, W.D., and Sutherland, W.M., 2000, Gemstones & Other Unique Minerals & Rocks of Wyoming - A Field Guide for Collectors: Wyoming Geological Survey Bulletin 71, 268 p.

Geisha dressed in jade - colored pencil sketch.
Hausel, W.D., 2006, Minerals & Rocks of Wyoming, A Guide for Collectors, Prospectors and Rock Hounds, WSGS Bulletin 72, 125 p.

Hausel, W.D., and Sutherland, W.M., 2006, World Gemstones: Geology, Mineralogy, Gemology & Exploration: WSGS Mineral Report MR06-1, 363 p.

Hausel, W.D., 2009, Gems, Minerals and Rocks of Wyoming. A Guide for Rock Hounds, Prospectors & Collectors. Booksurge, 175 p.

A great majority of in situ jade is found north of Jeffrey City (T30N, R92-93W). Many were prospected in the past and thus most are now marked by old prospect pits. Look on Google Earth for prospect pits and then visit them.


Massive emerald green Wyoming jade
Jade was at one time highly sought after by Wyoming prospectors. But much of the high-quality easily found, emerald-green and translucent jade was found in Tertiary conglomerates at Crooks Gap. Lower quality light-green jade was found in place to the north of Crooks Gap in the Granite Mountains, but the source of the valuable emerald green was never identified and remains to be found. In the 1930s and 1940s, many jade boulders weighing several hundred pounds were found near Jeffry City in central Wyoming.

Jade carvings
Jadeite has never been found in Wyoming. It forms at high-pressure and low-temperature from near surface to depths as great as 30 miles. Geologically, it is found near convergent continental margins (where there is considerable pressures and temperatures from tectonic stress), and forms by fluid interaction with serpentinizing peridotite at depth. It occurs in veins and masses within metamorphic rocks, particularly albitite, actinolite schist and/or serpentinite. Most jadeite is found in highly faulted, subduction-related serpentinite or m̩lange along major fault zones Рsuch as in California.

Extraordinary specimen of polished jade from Wyoming with rind
Only three countries produce jadeite on a commercial scale: Burma, Guatemala and Russia. The jadeite from Guatemala is granular, mottled, and opaque. Burmese jadeite has more intensely saturated colors of deep-lavender to emerald- imperial green. Jadeite from Russia, although generally dark-colored, tends to sit between the Burmese and Guatemalan jadeite. Jadeite has not been identified in Wyoming.

Nephrite jade is produced primarily by Canada. Wyoming produced large quantities of fine nephrite in the past, but there is no longer commercial production. Russian nephrite was exported to China in the past and most Russian jadeite was sold through markets in Hong Kong as Burmese jadeite. In Eastern Turkistan, the jade market is strictly controlled by the Chinese government and only government buyers can purchase jade at the price set by the government.




Did you guess which was the serpentinite? The specimen to the left has small spots that are magnetic that can be detected using what is known as a pencil magnet (see http://www.minerox.com/). With some effort, it can also be scratched with a pocketknife.
Intrigued by all of the treasures out there in the world to be found? There are geological hints on where and how to find jade and hundreds of other mineral deposits. Many of these are described in my newsletters at GEMHUNTER and are also described in much greater detail in my new book on Gems, Minerals and Rocks available at Booksurge and Amazon.
 

Wow, can you believe this specimen? Jaded brains. That's right, the last moron I worked for at the Wyoming Geological Survey had his brains removed and we examined them under a microscope and found them to be replaced by jade (just kidding - about the replacement).


My good friend, Dr. J. Dave Love (RIP) sits on large Wyoming jade boulders