In part one of the jade series, we noted that the name ‘jade’ is a commercial term used for two minerals: jadeite and nephrite. Last month we focused on jadeite; this month, we focus on nephrite.
However, it has a higher tenacity and is regarded as the ‘toughest’ of gems.
This property of toughness makes it suitable not only in a range of jewellery, but also for use in gem carvings and decorative items.
Nephrite is an opaque to semi-translucent mineral with a vitreous to somewhat greasy lustre. Most consumers will be familiar with green nephrite, with its colour ranging from pale to dark green.
However, the gem has other colours: white, yellow, brown, grey and black, and a rare blue. The ‘mutton fat jade’ of China is actually nephrite.
Like its relative jadeite, nephrite is mostly found in the form of pebbles and boulders near streams and rivers.
This location is attributable to the toughness of the mineral because these two minerals do not weather easily. But as the two form under different geologic conditions, they are not found together in the same location.
Nephrite jewellery often features beads and carvings with animal and floral motifs. High quality nephrite may be cut as cabochons, and its strong colour and opacity make the gem ideal for use in rings and pendants.
Nephrite that is translucent with a solid green colour is the most valuable. Mottling of colour or the presence of dark mineral inclusions lessens the gem’s value.
Nephrite is a more common mineral than jadeite, and its major sources are New Zealand, Mexico, Peru, British Columbia and Taiwan. It is the official state mineral of Wyoming.
To the Maori of New Zealand, nephrite – called pounamu or greenstone – is an important gemstone found on the South Island around Otago.
It has great cultural significance, used not only for adornments but also for practical uses, including making tools and weapons.
It is often worn as a pendant called a Hei-tiki, which can be a simple smooth polished piece or carved into traditional Maori symbols of good fortune.
As with jadeite, nephrite has many imitants. Because it is tougher than jadeite, nephrite is more difficult to dye, so its imitants tend to be other kinds of mineral that may be dyed green, or minerals that are naturally green.
A gemstone that can look similar is bowenite, a member of the serpentine mineral group.
However, unlike nephrite, the green colours of bowenite tend to look rather yellowish or blueish and may contain patches of white. Bowenite is softer than nephrite, with a hardness of 5.5 on Mohs’ scale.
Other imitants of jade include amazonite, which is a blue-green variety of feldspar, aventurine, a cryptocrystalline variety of quartz, and massive grossular garnet.
Jade jewellery, whether it be jadeite or nephrite, looks its best when kept clean. Wipe it gently with a soft cloth dipped into soapy water – don’t scrub or you will dull the surface! Then use a cloth wetted with just water to wipe off any soapy residue.