Nephrite

Nephrite is one of the two stones called “jade”; the other is jadeite. It is made of fibres of the minerals tremolite and actinolite, too fine to see, matted together like felt. This texture gives it great toughness, meaning resistance to breaking. In China, New Zealand and Taiwan it has been used for tools, jewellery and works of art for thousands of years.

Carving and art: Because it can be worked very thin without breaking, it is used for carved vases, sculptures, seals and ceremonial objects; in China the tradition goes back thousands of years. Jewellery: It is made into bangles, pendants, beads and ring stones. Prehistoric tools: In the Stone Age it was used for axes, chisels and weapons from Europe to New Zealand; nephrite tools have been found in ancient lakeside settlements in Switzerland. The Māori made tools, weapons and ornaments from pounamu.

It has a hardness of 6–6.5 on the Mohs scale. It can scratch glass; a steel knife scratches it only with difficulty. Its specific gravity is 2.9–3.1 g/cm³.

Its best-known localities: Cowell, Eyre Peninsula, South Australia; Eastern Sayan Mountains, Buryatia, Russia; Dease Lake–Cassiar area, British Columbia, Canada; West Coast (Arahura River), South Island, New Zealand; Hotan (Khotan), Xinjiang, China.

Polished, it has a soft greasy to glassy lustre; unworked surfaces are dull. It ranges from translucent to opaque and is often mottled or spotted. With a hardness of 6–6.5, a steel knife does not scratch it easily. Its real strength is toughness: thanks to its fibrous structure it is hard to break with a blow, and broken surfaces look splintery or granular. It is slightly lighter than jadeite (specific gravity about 2.95, against about 3.3 for jadeite); laboratories tell the two apart by density and refractive index. Serpentine and bowenite look similar to nephrite and are often sold as “jade”, but they are generally softer. Some of the stones called pounamu in New Zealand are bowenite rather than nephrite.

On the “street to diamond” value ladder it sits on step 6 of nine: Fine ornamental and collector stone. Colour and texture matter most: in China the translucent, pure white to pale yellowish “mutton-fat” jade is the most sought after, while green nephrite should have an even, lively, spotless colour. A fine, tight texture, a good polish and freedom from cracks and blotches raise the value. In carvings, the quality of the craftsmanship and the age of the piece often count for more than the stone itself. Untreated stone is worth far more than dyed or resin-impregnated material.

In 16th-century Europe nephrite was believed to help with kidney pains and colic; that is why it was called lapis nephriticus, Latin for “kidney stone”, and why the name “nephrite” comes from the Greek nephros, “kidney”. In Māori culture pounamu is a treasure (taonga); it is believed to absorb “mana”, spiritual power and prestige, as it passes down the generations, and heirloom pieces are sometimes named after former owners. There is no scientific evidence that nephrite helps kidney disease or colic; anyone with a kidney complaint should see a doctor rather than rely on a stone. The place of pounamu in Māori culture, by contrast, is not a health claim but a cultural and spiritual value handed down over generations. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.