The brief information provided by local tourist sites on the types of stones that can be found on Gemstone Beach often mentions sapphires. “Part of Te Waewae Bay, Gemstone Beach is a popular destination for rock hunters and visitors interested in geology, ‘gems’ (including sapphires) are known to be found” (Riverton website). “A few hours beachcombing could easily yield gems such as hydrogrossular, jasper, fossil worm casts and the elusive sapphire” (Heritage Trail website). I’ve been aware for some time of this view that sapphires could be found on Gemstone Beach. But in my many visits there, they have always been truly elusive to me. I don’t think I’ve ever seen one. And would I know one if if I did? What do they look like? How rare are they? Has anyone actually found one?
Then last year my sister from Gore showed me a newspaper cutting. It was a short piece on Gemstone Beach by columnist Lloyd Esler in the “Southland Times” in March 2018 which also included a photograph of two sapphires from the Beach (see photo at top of this Post, far left hand side). Esler wrote: “The best known of the ‘gemstones’ are grossular garnets which are distinguished by their gloss and weight, and sapphires with their characteristic colour and extreme hardness… The nearest thing to a ‘precious’ stone from the beach is a sapphire but these ones are not gem quality.” The Riverton Museum Te Hikoi also has three small stones labelled “Sapphire” in its display of stones that can be found on Gemstone Beach (see photo at top, second from left). And the photo at the top of this Post, second from right, is a photo of an “Orepuki sapphire” from the Flickr page of the Otago Rock and Mineral Club. It is accompanied by the following description: “The blue colour is sapphire which is combined within the structure of a hydrogrossular garnet”. The photo at top, far right, is is an example of a cut precious gem sapphire, but a lot of naturally occurring sapphire is nowhere near such quality.
The New Zealand geologist Jocelyn Thornton produced an excellent booklet “Gemstones” (1985), now freely available online. It has a page on “Beryl, tourmaline, corundum (ruby and sapphire)”. Two samples of sapphire are photographed: “Rare blue sapphire occurs with the tourmaline at Richmond Flat… Even rarer are waterworn pebbles found on the beach on at Orepuki in Southland. Their source is unknown.” She includes a photo of an Orepuki sapphire (circled on the photo at far left below). In her book, “The Field Guide to New Zealand Geology” (2003), Thornton refers to the blue corundum at Richmond Flat in Nelson as “dull” and “extremely rare” (page 49). She also notes that “ruby rock” or Goodletite, found only in a small area near Hokitika on the West Coast of the South Island, sometimes contains tiny crystals of “bluish sapphire” (page 70). Below, second from left, is a map of Goodletite distribution from a 1996 article in the “Journal of Petrology” by R. Grapes and K. Palmer (“Ruby-sapphire-chromium-mica-tourmaline rocks from Westland, New Zealand“) and below, second from right, is a photo of Goodletite from Mindat.org. The rock is named after William Goodlet, who recognised it as an unusual stone when visiting the Rimu gold workings in 1892. (Mindat.org states that Goodletite has also been found at “the Mont D’Or Mine at Ross, Olderog Creek, Whitcombe Valley, and the Taipo River”.) The photo on the far right below is a slice of Goodletite made into jewelry.
What is sapphire? Sapphire is a variety of corundum (see photos below, the two to the left), which is a crystalline form of natural aluminium oxide (Al2O3) (a metamorphic variant of bauxite) and its purest colourless form is very rare. Composed of only aluminium and oxygen, it requires a growth environment free of silicon to form. It was not until the 18th century that it was clearly established that sapphires and rubies are the same mineral. As Gemporia points out, various trace elements that enter the corundum during its formation produce all the exquisite and unique varieties of sapphire. Blue sapphire is coloured by the presence of titanium and iron, for example, and it is the balance of these impurities within the stone that causes such a wide range of blue tones, from bright, clear cornflower blues to deep dark midnight blues. Titanium and iron need make up only a few hundredths of one per cent of the corundum to make a typical blue sapphire. As Lin Sutherland in “Gemstones of the Southern Continents” (1991) notes, when these two elements replace aluminium atoms and sit side by side, they share their electric charges. “This energy state absorbs a broad band of the light, leaving only blue and violet blue. If the two elements sit slightly further apart, the absorption changes and lets through blue-green” (page 105). Iron alone can lead to yellow and green colours, orange hues need iron and chromium, and vanadium causes purple hues. The photo on the far right below, from Sutherland’s “Gemstones of the Southern Continents” (1991), illustrates the wide variety of coloured sapphires from one area in New South Wales.
Sutherland observes: “When chromium exceeds about 1 per cent in the mineral, atoms of this large and heavy element start to strongly absorb the shorter wavelengths of light. So red becomes the dominant colour. This earns the mineral [corundum] a new variety name, ruby” (page 44). Two photos of natural ruby crystals are below, left and middle, with a cut gem of ruby to the right.
Minerals.net states that Corundum is a very hard, tough, and stable mineral. For all practical purposes, it is the hardest mineral after diamond, making it the second hardest mineral with a rating on the Mohs scale of 9 out of 10. It is also unaffected by acids and most environments. Gem quality corundum is found in streams as its high density causes pieces to deposit within one local region and its hardness makes it resistant to weathering (Minerals Education Coalition). Non-gem corundum material is used as an abrasive because of its high hardness.
During my last visit to Gemstone Beach, in mid-June 2019, I met up with a fellow stone collector on the way back to the car park. He turned out to be Jack Geerlings from Winton. I had heard of him earlier this year when I had seen some of his polished stones for sale at the Good Studio, an art and gift gallery in Riverton (photo below). Jack has been ill and was on his first trip to Gemstone Beach for some weeks when I came across him. I was interested to hear about his work and we chatted for a while. Jack mentioned he had once found a nice sapphire on Gemstone Beach, after a small landslide had brought down part of the cliff there. He kindly asked if I would like to visit him and see his stones and workshop, and I jumped at the opportunity. I drove up to Winton two days later. Jack showed me his extensive collection of stones and his workshop. Right at the beginning, I asked to see his sapphire (3rd and 4th photos below) and he showed me two other small ones he had collected as well (5th and 6th photos below).
One of the things Jack talked about was the Rock Clubs he had been associated with. He has been actively involved with the Otago Rock and Mineral Club, for example, and it now seems to me that it is his large sapphire stone that is in the photograph on the Otago Rock and Mineral Club Flickr page. Jack was very generous with his time and shared the stories behind many of his stones. He allowed me to takes photos of his large and diverse stone collection, which includes many agates and a lot of petrified wood.
As a result of seeing and handling Jack’s fine sapphire stone, I now stand a better chance of recognising one should I stumble across it on Gemstone Beach in the future. However, “rare” and “elusive” are likely to remain its key characteristics.