Nephrite is one of two gem materials, nephrite and jadeite, that are known as jade. They have a somewhat similar colour range and a tough, microcrystalline structure. Both have been used as carving materials throughout history. Of these two minerals, only nephrite is found in Australia.
- Chemistry: Calcium magnesium/iron silicate
- Hardness: 6.5
- Refractive Indices: Approximately 1.61
- Specific gravity: 2.90 - 3.10
Nephrite is a magnesium iron calcium silicate, with iron as the colouring agent. A high iron content causes deep green to black colours while a low iron content results in lighter shades, including the so-called 'mutton fat' jade.
Nephrite is a popular name given to gem quality tremolite, one of the amphibole group of minerals. Amphibole minerals have elongated, fibrous crystals and this fibrous, interlocking structure gives nephrite its inherent toughness and enables it to take on a high polish.
Australia has a large, mined deposit of nephrite at Cowell, South Australia and a smaller one near Tamworth, New South Wales. Tamworth nephrite is generally lighter in colour than Cowell material.