Information
INTRODUCTION JADE
Jade comes in two varieties- Jadeite and Nephrite, Jadeite being the more valuable of the two Jadeite – used by the Aztecs from sources in the Andes, Jadeite was later discovered in Burma (Myanmar) about 300 years ago and became popular with the Chinese emperors. Burma still the major source today, although marketed through Hong Kong. More recently it has also been found in California and Russia, through not of gem quality.
JADE
COLOR,CLARITY & CUT
Jadeite is found in a range of colours: bright green, purple, orange, brown, black & very rarely ,red. It varies from translucent to opaque; the most valuable is the bright translucent emerald green called ‘Imperial Jade’. Next is the purple, the least popular colour is the dark olive green-grey.
JADE GEMSTONE PROPERTIES:
| Jadeite Jade | |
| Colors | Various shades of green, lavender, white, colorless, brown, orange |
| Composition | NaAlSi2O6 |
| Hardness (Mohs) | 6.5–7 |
| Specific Gravity | 3.34 (+ 0.06, –0.09) |
| Refractive Index | 1.666–1.680 (±0.008); spot RI 1.66; birefingence usually not measurable |
| Optic Character | DR, Biaxial; aggregate polariscope reaction |
| Spectrum | Generally line at 437 nm; Cr-green may have lines at 630, 655, 690 nm |
| Crystal System | Monoclinic; occurs as massive polycrystalline aggregates |
| Fracture | Granular to splintery |
| Pleochroism | None |
| Phenomena | None |
| Handling | No special care needed for untreated jadeite; treated jadeite may be damaged by ultrasonic and/or steam cleaning; solvents, acids |
| Enhancements | Most jadeite is wax dipped; some jadeite is dyed and/or bleached and then polymer-impregnated. |
| Synthetic available? | Yes, but quite rare in the market |
VALUE:
The more opaque the stone, the lower the value. Off-colour Jadeite is commonly dyed to simulate Imperial Jade but its opacity belies the truth. Improvement is also achieved by bleaching and impregnating with resin, although there are doubts as to the permanency of this procedure. Jadeite with hardness of 6 1/2to 7 and an SG of 3.33 is slightly harder than Nephrite but it is less tough. It has a bright glassy shine.
Most gems are cabochon cut and quite often waxed to improve the polish, but this may be damaged by heat and overzealous cleaning.
The latest classification of Jadeite Jade is
‘A’ Jade – natural untreated
‘B’ Jade – polymer treated
‘C’ Jade – stained
‘B & C.’ Jade –polymer treated and stained
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NEPHRITE
NEPHRITE is found in very many locations around the world and is not used in jewellery as much as jadeite. It is used mainly for carvings. Brown shading of parts of the rock is caused by oxidation and this is used by carvers to attain a two-colour effect.
Nephrite Jade comes in fewer colours than Jadeite, white (‘mutton fat jade’),dull green (‘spinach jade’)often with black spots of magnetite, brilliant green and yellow ,which is the most valuable.
Treatments are basically similar for nephrite as for Jadeite: dyeing ,waxing and bleaching are common. It has a hardness of 6 1/2 (Mohs) and an SG of approximately 3.0.It is an extremely tough material, which makes it difficult to mine.
ORIGINS & IMITATION
The main sources are now New Zealand, the USA, Siberia, South America & Silesia. There are very many simulants of Jade: bowenite (a form of serpentine, chrysoprase, stained chalcedony, massive Emerald, hydro-grossular Garnet, Amazonite, Prehnite, Connemara marble and verde antique). Jade shows green under the Chelsea Filter where some stimulants, particularly Prehnite, show red. However, certain Jades contain chromium and will also show red. A Hodgkinson’s special filter can be used to identify dyed jade. This reinforces the doctrine of ‘buy from a reliable source’, not from street traders, and make sure that the receipt states that it is genuine untreated Jade.
In South America’ antique’ Jade articles are made from current Jade & aged artificially by heat treatment to simulate the oxidation found on genuine old Jade: very convincing.
NAME, FAME & LEGEND
The name “Jade” is derived from piedra de hijada, the Spanish name for Jade. The Spanish adventurers in the time of Cortes brought back the jade pieces which they found among the Indians. The Spanish translation means “stone of the flank or loins,” or “colic stone.” It is believed that the flat polished pebbles with rounded edges resembled the kidneys, and would, therefore, be efficacious in disorders of that organ. Hansford states that the Spaniards knew the stone as piedra de los rinones (‘kidney stone’), a name which was translated into Latin as Lapis Nephriticus and this gives the word Nephrite.
In 1863, French mineralogist Alexis Damour analyzed bright green jades from Burma. When he found these samples to be different from what was called Chinese Jade (usually amphibole Jade, or Nephrite), he named the mineral Jadeite.
