Nephrite

nephrite
Tumbled nephrite

Nephrite, recognized as a separate type of jade since 1863, is found as aggregates of fibrous amphibole crystals. These form an interlocking structure tougher than steel, hence nephrite’s popularity as a material for carving – first for weapons and later for ornaments. Colors vary from a dark green, iron-rich nephrite to a cream-colored, magnesium-rich variety. Nephrite jade may be homogeneous in color, blotchy, or banded.

Nephrite jade has been carved by the Chinese for over 2,000 years, although the raw material was probably imported first from Turkestan in Central Asia, and later from Burma. Other localities include Siberia (dark green boulders, often with black spots), Russia (spinach-colored stones), and China itself. Nephrite jade is also found in various rocks in the North and Sought Islands of New Zealand (pieces carved in the 17th century include Maori clubs called meres). Other localities include Australia (black nephrite), the USA, Canada, Mexico, Brazil, Taiwan, Zimbabwe (dark green), Italy, Poland, Germany, and Switzerland.

Nephrite may be confused with bowenite serpentine, may be imitated by composite stones, or dyed to improve color.

Nephrite Pictures

Tumbled nephriteNephrite braceletNephrite Buddha statue

Cause of Color :
  • More iron content – deeper green.
  • More magnesium content – creamy brown.
  • Chatoyancy is due to the presence of parallel fibers.
Chemical Composition :

Calcium Magnesium Silicate + Fe2+, Ca2(Mg,Fe)5(OH)2(Si4O11)2

Classification / Type :

Belongs to the tremolite – actinolite series of the amphibole group of minerals.

Crystal System / Forms :

Monoclinic System / Cryptocrystalline, boulders commonly covered with a brown layer due to oxidation of iron content.

Cuts & Uses :

Cabochons, beads, carvings, etc.

Hardness : 6.5
Lustre : Vitreous to greasy.
Magnification :

Brownish veins seen due to oxidation of iron content, black crystal inclusions.

Optic Character :

Anisotropic, D.R.; Aggregate (A.G.G.)

Pleochroism : None.
Refractive Index / Birefringence :

1.606 – 1.632 (Spot R.I.: 1.610) / 0.026

Simulants (with separation tests) :

Jadeite (R.I., S.G., structure, spectrum), Serpentine (R.I., S.G., lustre, hardness), Idocrase (R.I., spectrum, structure), Hydrogrossular Garnet (R.I., S.G.), Prehnite (R.I., birefringence, structure), Aventurine Quartz (R.I., S.G., structure, spectrum), Maw-sit-sit (color, structure).

Sources :

Russia, China, New Zealand, Australia, Canada, Poland, U.S.A. (Alaska, Wyoming), Brazil, etc.

Specific Tests :

Consists of an interlocking mass of fibrous crystals making it one of the toughest minerals (but not the hardest mineral), more than jadeite.

Spectrum :

In general not characteristic, but may show weak lines at 460nm, 498nm, 509nm, 690nm.

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