玉   Types of Jade  


Cochise College Student Papers on Geology
 Paper on Jade by George Soong

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            Nephrite is a form of jade which is a silicate of calcium and magnesium, containing traces of iron, aluminum and sodium and belongs to the tremolite-actinolite series of the mineral family amphibole.  Colors are green, white or gray.  Lighter colors are closer to tremolite and darket colors are near actinolite.  Nephrite is composed of fibrous needles in an tightly woven arrangement.  Nephrite has a hardness of 5.5 to 6 on the mohs scale of hardness.  The cleavage of Nephrite is perfect in two directions at close to 60- and 120-degree angles.  Nephrite is formed in rocks subjected to low-grade metamorphism.

           

            Jadeite  is a form of jade which is a silicate of sodium and aluminum, containing traces of calcium, magnesium, potassium, iron and chromium.  It belongs to the augite family of the pyroxene group.  Colors can be shades of green, lilac, blue, pink, white, yellow, black, and a unique black with natural precious metal included.  Jadeite is composed of interlocking crystals.  It has a hardness of 6.5 to 7 on the mohs scale of hardness.  It is harder and tougher than steel.  The cleavage of Jadeite is poor in two directions at near 90 degree angles.    Unlike nephrite, jadeite is in rocks once subjected to deep-seated metamorphism and subsequently uplifted and eroded.  Below is a picture of a California jadeite under a microscope using polarized light.  Interlocking crystals can be seen clearly with the aid of a microscope.   

 

A comparison chart between Nephrite and Jadeite

 

Nephrite

Jadeite

Chemical Composition

Ca2(Mg, Fe)5Si6O22(OH)

NaAISi2O6

Mineral Composition

Amphibole Group

Pyroxene Group

Crystalline Structure

Fibrous, tightly woven

Interlocked Crystals

Hardness

5.5 6

6.5 7

Refractive Index

1.62

1.65 1.66

Polished Surfaces

Smooth with a waxy sheen

Hard and lustrous

Cleavage

Two directions at close to 60- and 120-degree angles.

Two directions at near 90 degree angles

 

Produced by George S.

2003 - 2008