The term nephrite is used to distinguish a gemstone that is associated with jadeiteas being part of the jadefamily. Actually they are two different stones with some distantly similar properties, but due to their similarities in color and use in carvings in China they have come to be related to each other if in name only. Nephrite is the less prized but more common of the two types of jade and may be distinguished by its splintery fracture and oily luster. Nephrite usually has green color of different shades and is generally opaque.

The name nephrite is from the Greek nephros (kidney) via Latin Lapis nephriticus (kidney stone), and appears to have been based on the ancient belief that it served as a remedy so far as alleviating or curing kidney diseases. 

The nephrite variety is composed of fibrous crystals inter-twinned in a very tough compact mass. Nephrite occurs in low-grade (formed under low-temperature, low-pressure conditions), regionally metamorphosed rocks. It also occurs as a product of metamorphism of magnesium-rich limestone. Important deposits occur in China, Siberia, New Zealand, Switzerland, Alaska, and Wyoming.

Over the ages, nephrite, apparently because of its great toughness, found wide use as tools, including sacrificial knives and weapons, in China , central Europe, New Zealand and in the Americas , especially in what are now known as Guatemala , Mexico and the southwestern United States . It is often used as a decorative stone or for carvings. The sarcophagus for Czar Alexander III was carved from nephrite jade.

Characteristics:

Chemistry: Ca2(Mg,Fe)5Si8O22(OH)2
Hardness (Mohs scale): 6-6.5
Density: 2.9 – 3.02
Refractive index: 1.600 – 1.627
Dispersion: none
Crystal system: monoclinic
Transparency: translucent to opaque
Luster: oily, esp. on polished surfaces
Fracture: splintery