Nephrite Jade

Hardness: 5-6.5 (Mohs scale); Color: Typically dark green to black, sometimes brownish or reddish; Luster: Vitreous to sub-vitreous, dull in massive forms; Crystal Structure: Monoclinic; Cleavage: Good prismatic cleavage often visible; Specific Gravity: 3.2-3.6. Often appears as lustrous, elongated crystals or in massive, compact forms. The specimen in the image appears to be a tumbled or water-worn piece of Nephrite Jade due to its dark, somewhat waxy luster and rounded shape.

Nephrite is a metamorphic mineral that forms under moderate to high pressure and temperature conditions. It originates from the metamorphism of calcium-rich igneous rocks (like gabbro or basalt) or sedimentary rocks (like dolomite), where calcium-magnesium-iron silicates are formed. It often occurs in serpentinite rocks. Its geological age varies depending on the specific metamorphic event, ranging from Precambrian to Cenozoic.

Historically and presently, nephrite is highly prized as an ornamental stone. It's extensively used in carving for sculptures, figurines, and ritual objects. In jewelry, it's used for cabochons, beads, and sometimes faceted. Due to its toughness, it was also used for tools and weapons by ancient civilizations. Its value is determined by color, translucency, and the quality of carving.

Nephrite has been used for tools, weapons, and ceremonial objects by various ancient cultures, particularly in China (where it's considered the 'Stone of Heaven') and Mesoamerica. It's often associated with good luck, health, and immortality. The term 'jade' broadly refers to two distinct minerals: nephrite and jadeite, which have different chemical compositions and crystal structures but similar appearances.

In the field, nephrite can be identified by its exceptional toughness (resistance to breaking/chipping, not necessarily hardness), waxy to greasy luster when polished or wet, and characteristic dark green to black color. It's often found in association with serpentinite belts in mountain ranges. Major localities include British Columbia (Canada), Wyoming (USA), Siberia (Russia), Xinjiang and other regions (China), New Zealand (Maori greenstone), and parts of Australia. For collectors, look for pieces with good color saturation, translucency, and a lack of visible inclusions or cracks. The Mohs hardness test (not scratching with a steel knife, which is typically 5.5) can help distinguish it from softer look-alikes.