Sunday, 18 December 2016

Jade

What is jade?

Jade is best known as a green ornamental stone. Its colours varies from light to dark green, but it may also be other colours such as white, gray, and purple. Jade is actually the gemstone name for two different mineral forms, Jadeite and Nephrite. These two minerals can be identical in appearance and are similar in their physical properties, and until modern times no distinction was made between the two different types of Jade. While Nephrite is generally only green, cream, or white, Jadeite colours can range through the colour spectrum with more exotic colours.
"Jade" is a cultural term used for a very durable, and often beautiful, material that has been fashioned into tools, sculptures, jewellery, gemstones, and other objects for over 5,000 years. It was first used to manufacture axe heads, weapons, and tools for scraping and hammering because of its toughness.
Then, because some specimens had a beautiful colour and could be polished to a brilliant luster, people started to use jade for gemstones, talismans, and ornamental objects. Although most people who think of jade imagine a beautiful green gemstone, the material occurs in a wide variety of colours that include green, white, lavender, yellow, blue, black, red, orange, and gray.

Nephrite and jadeite

Nephrite and jadeite were used from prehistoric periods for hardstone carving. Jadeite has about the same hardness as quartz. Nephrite is slightly softer, but is tougher (more resistant to breakage) than jadeite. It was not until the 19th century that a French mineralogist, Alexis Damour (1808-1902), determined that "jade" was in fact two different minerals.
Among the earliest known jade artifacts excavated from prehistoric sites are simple ornaments with bead, button, and tubular shapes. Additionally, jade was used for axe heads, knives, and other weapons, which can be delicately shaped. As metal-working technologies became available, the beauty of jade made it valuable for ornaments and decorative objects. Jadeite measures between 6.0 and 7.0 Mohs hardness, and nephrite between 6.0 and 6.5, so it can be worked with quartz or garnet sand, and polished with bamboo or even ground jade.

History and Introduction

Jade is an umbrella term that encompasses a variety of gemstones, but the only pure forms of jade are jadeite and nephrite. The history of jade goes back several thousand years when jade was first used to make weapons and tools because of its toughness. The Mayans and Aztecs regarded jade highly and the name "jade" originates from the Spanish "piedra de ijada", meaning "stone for the pain in the side". It was named in this way after Spanish explorers saw natives of Central America holding pieces of jade to their sides, believing that it could cure ills. The Chinese refer to jade as "yu", which means "heavenly" or "imperial". Therefore, it is considered to be the imperial gem in Chinese culture. In China, jade was found in the tombs of Shang kings.
Jade also plays a part in the history of New Zealand. It is found on the South Island and has been treasured for many years by the Maoris of New Zealand, who call it "pounamu", "greenstone" or "New Zealand jade". Pounamu has been made into Maori tools, such as chisels and fish hooks, and weapons, such as short clubs and ornaments. This New Zealand jade is usually nephrite. Spinach-green nephrite from the Lake Baikal region of Russia is known as "Russian jade". Jadeite is the rarer of the two varieties of jade, and as a result it is more precious. The most valuable variety of jade is a striking and even emerald green jadeite, known as "imperial jade".

Jadeite, Nephrite, and Artisans

China has been the leading producer of jade objects for over 5,000 years. A few hundred years ago, master Chinese craftsmen who worked with jade daily recognised that some of the jade obtained from Burma (now the Union of Myanmar) was different. It was harder, denser, worked easier, and produced a higher luster upon polishing. It gradually became the form of jade preferred by Chinese artisans and the jade most highly prize by the Chinese people. They realised this long before scientists differentiated jadeite and nephrite in 1863.
Unknowingly, Chinese craftsmen had distinguished jadeite from nephrite and appreciated it enough to pay premium prices for jadeite. However, they didn't have the knowledge and equipment of chemistry and crystallography to distinguish them in a formal way.
Rarely, the Chinese craftsmen encountered fine-grained jadeite with a bright translucence and a rich, uniform green colour. This beautiful material was given the name "Imperial Jade" and regarded as the stone of highest quality. At that time in China, ownership of Imperial Jade was reserved only for the Emperor. Now, anyone who can afford it can own Imperial Jade. The best specimens can cost more per carat than high-quality diamonds.

Early Use of Jade in Tools

People have used jade for at least 100,000 years. The earliest objects made from jade were tools. Jade is a very hard material and is used as a tool because it is extremely tough and breaks to form sharp edges.
Most jade does not have a colour and translucence that is expected in a gemstone. However, when early people found these special pieces of jade, they were often inspired into crafting them into a special object.
"Toughness" is the ability of a material to resist fracturing when subjected to stress. "Hardness" is the ability of a material to resist abrasion. Early toolmakers took advantage of these properties of jade and formed it into cutting tools and weapons. It was used to make axes, projectile points, knives, scrapers, and other sharp objects for cutting.

Use of Jade as a Gemstone

Jade is a durable, colourful material that can be worked into shapes and given a high polish. These properties make it a very desirable gemstone. Jade has been used to make a variety of jewellery items such as pendants, necklaces, rings, bracelets, earrings, beads, cabochons, tumbled stones, and other items.
These jewellery items are often made of solid jade, combined with other gems, or placed in settings made from gold, silver, or other precious metals. In addition to jewellery, jade is used to make small sculptures, ornaments, religious art, and small functional objects.

Identifying Jade

Jade can be distinguished from other similar materials by its hardness and density. There are a lot of other materials fraudulently sold as jade and it is difficult to identify jade by outside appearance. The most reliable method of identifying jade from other substances is by testing its specific gravity. A simple test to distinguish jadeite from nephrite is a chime test. Nephrite emits a musical tone when it is struck, whereas jadeite does not.

Jade: Origin and Gemstone Sources

Nephrite is more common than jadeite and deposits have been found in New Zealand, Australia, Brazil, China, Canada, Zimbabwe, Russia, Taiwan, Alaska and Poland. The main source of jadeite is Myanmar (Burma), which is also the only source of imperial jadeite. Jadeite is also found in Japan, Canada, Guatemala, Kazakhstan, Russia, Turkey, Cuba and the USA.

Other Materials Confused With Jade

A number of other minerals and materials that are commonly cut and polished are easily confused with jade. All of these materials can have a colour, luster, and translucence that is very similar to jade so similar that the average person is unable to recognise them. These materials are often used to manufacture cabochons, beads, and other objects in the same style as jade. They sometimes enter the jade market without distinction.
Chalcedony is a translucent variety of microcrystalline quartz that occurs in a range of colours similar to jade. Chrysoprase is a bright green chalcedony coloured by chromium that, when cut into cabochons, beads, and small sculptures, will look very similar to jade. Chalcedony occurs in a variety of other translucent colours such as black, lavender, yellow, and orange that can look like the color varieties of jade. Chalcedony can be a very close gemstone look-alike with jade. It can be differentiated from jade using is lower specific gravity and by a variety of instrumental methods.
Serpentine occurs in a variety of wonderful translucent to nearly transparent green and yellowish green colors that look very much like jade. It is a metamorphic mineral that is often found in the same geographic areas and same types of rocks as jade. Serpentine is significantly softer than jade and also has a much lower specific gravity.
Vesuvianite, also known as idocrase, is another jade look-alike that is very difficult to distinguish from jade without laboratory testing. It has similar hardness, specific gravity, and physical appearance. It is not nearly as tough as jade and will break easier - but that requires destruction of the specimen.
Maw Sit Sit is a rock with a bright chrome-green colour mined in Myanmar. It has a very similar appearance to jade. Maw sit sit is composed of jadeite, albite, and kosmochlor (a mineral related to jadeite). It is used to cut cabochons, beads, and make small sculptures, and is easily confused with jade.
Hydro-grossular Garnet is a green massive variety of garnet that is usually green in colour with black markings. It looks so much like jade that in South Africa, where it is common, it is known as "Transvaal Jade." It is frequently cut into beads, cabochons, and small sculptures.
Aventurine is a trade name used for a green quartz that is often coloured by fuchsite inclusions. These typically colour the quartz a light to dark green colour and produce some aventurescent sparkle. Aventurine is sometimes confused with jade.

All of the above natural minerals and rocks can be confused with jade. Many people like them, enjoy them, and knowingly purchase them for that reason. It is important to know that these jade look-alikes, along with plastic and glass made into objects in the same style as jade, are abundant in the market place. Know what you are buying or purchase from a dealer you can trust if you are shopping for these items and desire jade instead of an alternative. Errors and deception are common.

Properties of Jade

Chemical FormulaNephrite: Ca2(Mg,Fe)5Si8O22(OH)2
Jadeite: NaAlSi2O6
ColourWhite, Blue, Red, Green, Yellow, Orange, Brown, Pink, Purple, Gray, Black, Banded, Multicoloured
Hardness6 - 7
Crystal SystemMonoclinic
Refractive Index1.60 - 1.67
SG2.9 - 3.7
TransparencyTranslucent to opaque
Double Refraction-0.027 (Nephrite); 0.013 (Jadeite)
LusterWaxy, vitreous
Cleavage1 or 2,2 - prismatic. Due to lack of visible crystals, cleavage is rarely observed.
Mineral ClassJadeite or Nephrite (Nephrite can be either Actinolite or Tremolite)