Gold not the only thing that glitters at Thames School of Mines

Visitors to the Thames School of Mines' Mineralogical Museum could be forgiven for thinking that the museum's treasures would all be about bright, shiny nuggets. But one of the most important and overlooked exhibits at the museum is a sample of gemrock absolutely unique to this country.

A blue-grey chunk of rock on a black piece of material.
The example of Ruby Rock at the Thames School of Mines. Photo: Heritage New Zealand Pouhere Taonga.expand/collapse

“Australia has its precious gems like opal, sapphire and diamonds, but Aotearoa New Zealand has ruby ​​rock – a gemrock all to itself,” says Thames School of Mines Property Lead, Elton Fraser. Both the School and Museum are cared for by Heritage New Zealand Pouhere Taonga.

“The rock incorporates red ruby, blue sapphire and crystal – all encased in emeral green Fuchsite. It's only found near Hokitika in the West Coast of the South Island, but we have a sample here at the Museum which always generates a lot of interest from visitors to the museum.”

The ruby ​​rock was originally discovered by miners on the West Coast in about 1892, and eventually found its way to Thames – more as a geological curiosity than anything else.

“At first glance the green rock appears brown and underwhelming, and for over a century miners threw it back whenever they found it as they didn't know what it was – nor did they understand its rarity,” he says.

That all changed in 2008 when the Gemological Institute of America and the Gemmological Association of Great Britain reclassified the unprepossessing rock to become New Zealand's only precious stone unique to this country.

Today it is described by some as the world's best kept secret.

“Ruby rock was originally called Goodletite after William 'Wullie' Goodlet, a laboratory assistant at the University of Otago. He was also an assistant to Professor James Gow Black – a mover and shaker who was a keen advocate for the establishment of mining schools around the country,” says Elton.

“With the Thames goldfield one of the richest in the world, it's no wonder that Black was a regular at the Thames School of Mines.”

Goodlet's calmness and trustworthiness was the perfect complement to Black's entertaining style of lecturing – which often combined science with showmanship that at times resembled magic shows more than lectures. Goodlet, who was somehow able to keep Black's exuberance in check, served as his right hand man.

Goodletite exists solely in the 50km2 Hokitika Glacier moraines – and nowhere else. The rock is a product of the straight fault line on the New Zealand West Coast; a geological feature that is itself unique in the world.

The gems grow in Chromium Mica 30km below the earth's surface at a constant pressure of 5 K-bar and a heat of 460 degrees celsius. Each rock requires constant pressure over three million years to form.

“Although the rubies themselves are not the best quality, it is the rock itself that possesses the rubies that are prized by collectors,” says Elton.

“So increasingly Hokitika is becoming renowned for its gold, greenstone – and now Goodletite.”

The Goodletite/ruby rock is just one of hundreds of samples on display at the wonderfully eclectic Mineralogical Museum with artefacts ranging from a model of Tower Bridge hand-carved from kauri gum through to an encased sample of blue asbestos – a naturally occurring fibrous silicate mineral .

“Both the Museum and the School of Mines are must-see attractions for people visiting or passing through Thames,” says Elton.

“They capture the essence of the Coromandel gold and mineral industries of the 19th century, and the important part they played in the economic, scientific and social history of New Zealand.”

Become a Time Traveler at the Thames School of Mines.

John O'Hare