New Zealand lacks precious gems such as diamonds, emeralds and sapphires, but it does have gemstones that are prized by collectors and used for making jewellery. By definition a gemstone is beautiful, durable and rare. Stones of gem quality are free of flaws, have good colour and are large enough to be worked into jewellery.
Most beach stones have been washed down a river and tumbled in the surf, and are already round and smooth. Gemstones are also found inland, but it is almost always necessary to obtain permission from the landowner to collect these.
Where to look
Finding gemstones requires knowledge of local geology, and patience. The best information on collecting stones in New Zealand comes from the various rock and mineral clubs, which hold regular meetings and exhibitions. Some clubs have negotiated permission to search for gemstones at localities which would otherwise be inaccessible. There is also a National Association of Rock and Mineral Clubs, which meets every year.
The main mountain ranges in both the North and South Islands are made of greywacke – a hard, grey muddy sandstone – and more than 95% of the river boulders that ultimately end up on the beaches are made of this rock type. Looking for gemstones is a matter of seeking out the small proportion of stones that are not greywacke.
Polished to perfection
Most stones look more interesting when they are wet or have been polished. Polishing entails the use of progressively finer grits to smooth the surface of the stone, with a polishing powder providing the final gloss. Most polishing of river and beach pebbles is done by tumbling: using a rotating or vibrating drum to polish many stones at a time. A cheap, but less satisfactory, alternative is to lightly spray smooth beach pebbles with a clear plastic coating.
The most prized and distinctive New Zealand gemstone is pounamu, which includes the mineral species nephrite and bowenite. Also known as greenstone or New Zealand jade, it is tough, workable, and beautiful when polished. Māori have traditionally made pounamu weapons, tools and ornaments, and used the stone for trading.
The main source of pounamu is the Arahura River, near Hokitika on the South Island’s West Coast. Pebbles of greenstone can sometimes be found on the beaches north of Hokitika, which is now a centre for pounamu craft work. Under the Ngāi Tahu (Pounamu Vesting) Act 1997, the ownership of all pounamu is administered by the Ngāi Tahu tribe.