A few days ago, I received a Comment on one of my New Zealand-related Blog Posts. It read: “I’m a rock lover, 70yrs old and now disabled. My dad’s favorite place on earth was New Zealand, WWII. I would LOVE to get a rock from your neck of the woods. Thank you, Karen [from Oklahoma].” So today I put in the mail to Karen seven stones from New Zealand’s Gemstone Beach in Southland. I found these stones there at different times over the last two or three years, and have tumble polished them to smooth them and give them a shine. Most stones take between about five and seven weeks to polish.
These stones come from the bottom of New Zealand’s South Island. The soldiers from the United States that were in New Zealand during World War Two were based mainly at the bottom of the North Island (see, for example, US Forces in New Zealand). Between June 1942 and mid-1944, there were somewhere between 15,000 and 45,000 American servicemen in camp there. The following has been observed about this time and these visitors to New Zealand, dubbed, mainly with affection, “The American Invasion”: “What gave the encounter its special quality was that the two societies were sufficiently similar to communicate easily, but sufficiently different to find each other intriguing. They were both former British colonies with a frontier past. Both believed in democracy, civil liberties and the capitalist way of life. Most people in both countries spoke English as their mother tongue. And in December 1941 the two nations, each with a Pacific coastline, found themselves at war with Japan. Yet there were also significant differences. The United States was a large and confident society of more than 130 million people, many of whom, a generation before, had been European slum-dwellers or peasants. New Zealand, by contrast, was a small, isolated country with 1.6 million inhabitants, about the population of Detroit, Michigan. It remained in many ways colonial in outlook, a Britain of the South which had some difficulty convincing the new arrivals that it was not ruled by Winston Churchill. [From US Forces in New Zealand]
The contemporary geography of New Zealand is introduced in Wikipedia as follows: “New Zealand (Māori: Aotearoa) is an island country located in the south-western Pacific Ocean, near the centre of the water hemisphere. It consists of a large number of islands, estimated around 700, mainly remnants of a larger land mass now beneath the sea. The [two largest islands] are the South Island (or Te Waipounamu) and the North Island (or Te Ika-a-Māui), separated by Cook Strait. The third-largest is Stewart Island (or Rakiura), located 30 kilometres (19 miles) off the tip of the South Island across Foveaux Strait. Other islands are significantly smaller in area. The three largest islands stretch 1,600 kilometres (990 miles) across latitudes 35° to 47° south. New Zealand is the sixth-largest island country in the world, with a land size of 268,710 km2 (103,750 sq mi). New Zealand is about 2,000 kilometres (1,200 mi) east of Australia across the Tasman Sea.“
The beach that these seven stones came from, Gemstone Beach, lies on the southern coast of the South Island. It is just a kilometre from the small village of Orepuki, and lies on Te Waewae Bay on Foveaux Strait. Banks of stones line the beach which is backed by cliffs. For the past few years, I have visited the beach three or four times a year as it has a fabulous mix of interesting stones, mostly brought down from the Eastern Fiordland Mountains by the Waiau River. For an account of Gemstone Beach and its stones, see this Post.
The first of the seven stones I am sending to Karen is a type of stone I find now and then on Gemstone Beach. It appears to be a very coarse-grained sandstone partially covered with a shiny reddish glaze.
The grains in it seem to include tiny clear crystals. When first seen on the beach, these stones look like red jaspers, but they are a type I have not yet identified. The glaze on them polishes well.
The second stone is a grey argillite stone, a fine-grained mudstone. It started as sediment at the bottom of the sea. It contains within itself the traces of ancient life, fossilised marks, tracks, burrows and deposits of small animals. At Gemstone Beach, these are called fossil worm-cast stones.
This type of stone is thought to be over 250 million years old, going back to the Permian Era. A wide diversity of trace fossil stones can be found at Gemstone Beach – I have even put together a small photo book about them. In his book “Terrain: Travels Through A Deep Landscape” (2015), the New Zealand writer Geoff Chapple recalls a search for examples of these trace fossils with a geologist. On page 253 he writes: “We looked for the tattooed rock, the trace fossils that Maori call mokomoko, and it took some time but we did find them, wetting down the face of a rock layer to reveal 270 million-year-old traces of burrowing worms that took the purple of their starting layer down into the pale depths beneath, or dragged their pale layer into some purple darkness below, working their primitive palette, thousands of small finger painters out of the Permian.” When I tumble polish these stones, I do so lightly, being careful not to wear away the traces in them.
The third stone is a small banded light brown pebble. Its light grey lines caught my eye on the beach.
One of the types of stones to be found on Gemstone Beach is banded argillite but most of these tend to be grey and to have better defined bands – here’s an example. It was not until I examined a close-up photo of the stone that I detected small clear quartz crystals in it. So I think this is likely to be quartz stone stained by a brown mineral in an unusual banded patterning. Stones experience millions of years of pressure, stress, heating, fragmenting and reforming, and this history produces an amazing complexity and diversity.
The next stone is a banded ignimbrite, a volcanic stone, a form of rhyolite. Its name has a New Zealand origin. It is one of my favourite stones because I imagine I can see deep space in it.
It is the presence of tiny gaseous pockets (which have been infilled by some mineral) that tells us this is a volcanic rock. Ignimbrite originates as the deposit of a pyroclastic flow, which is a hot suspension of particles and gases flowing explosively and rapidly from a volcano. New Zealand geologist Patrick Marshall originally came up with the term in the 1930s meaning “rain of fiery rock dust”. Some ignimbrite can be very loosely deposited, with lots of pumice in it. If it is buried at depth, it becomes compacted, gases and liquids are squeezed out, and it becomes solid and fine grained and glassy, like this stone. I can usually find at least a couple of these when I visit Gemstone Beach, but it can be hard to find specimens that are not cracked or chipped, and sometimes the tiny gas pockets prevent a smooth surface. I have been fortunate to find some that have polished well, including this other one.
The fifth stone, mainly white, has quartz in it, and could be a form of quartzite (a stone formed when heat and pressure is applied to fine quartz sand). The close-up photos certainly show tiny quartz crystals in it.
Quartz is silicon dioxide, one of the most common minerals in the Earth’s crust. It is also a key component in a wide array of minerals called “silicates.” One of the most common forms of quartz is crystals, either colourless and transparent or coloured (e.g., rose quartz and amethyst). Stones like this one results from the breaking down of quartz crystals and their reforming (metamorphosis), during which the quartz is mixed with other minerals which provide various colours. I don’t know enough to be able to identify what mineral has caused this quartz-based stone to be white in colour, but often it can be the presence of water.
The second last stone of the seven is another volcanic stone, originally with tiny gas pockets. But these pockets have been filled with a mineral. This makes the stone “amygdaloidal”.
An amygdale (sometimes called an amygdule) is an infilled vesicle or hole in a volcanic stone, the term coming from Latin for “almond” reflecting the almond-shape of many such vesicles. Hot water moves through the vesicles in the volcanic rock and, over time, various minerals precipitate out of the water to fill them (just like a stalactite is formed from dripping water). Sometimes, as with this stone, the amygdales later get put under heat and pressure and a variety of shapes can result. This Post features a Gemstone Beach stone that has circular amygdales while this Post has a stone with different coloured amygdales.
The final stone is a type that Gemstone Beach is perhaps most famous for, a hydrogrossular garnet, another stone with an interesting New Zealand connection.
Hydrogrossular garnet is a mineral that was first described in New Zealand, one of 13 minerals first described here. To explain: The basic constituents of stones are minerals. A mineral is a naturally occurring inorganic solid, with a definite chemical composition, and an ordered atomic arrangement. Sometimes a stone can be just one mineral, like quartz, and sometimes a stone can be a mix of minerals – granite, for example, consists of three main minerals, feldspar, quartz and mica. Every mineral is officially named, recorded and defined by the International Mineralogical Association. Currently there are 5,780 officially recognised minerals. Every mineral has a “type locality” which is the place it was found when it was first described and accepted officially as a new mineral (even though it will very likely be found in lots of other places). Hydrogrossular garnet was first described by New Zealander Colin Hutton, a geologist and later professor of mineralogy, in 1943. He analysed samples of the rock from the Nelson area which is its “type locality”. The other area that hydrogrossular garnet can be found in New Zealand is around Gemstone Beach, some 400 kilometres (250 miles) to the south (the two region used to be side by side but the the movement of the alpine fault has placed them at opposite ends of the South Island – see this Post).
Hydrogrossular stones often feel waxy and some are partly transparent. “Grossular” derives from the Latin word for gooseberry, referring to the light-green colour of many hydrogrossular garnets (this is explained more in this Post). However, other minerals get mixed in, and white and brown are two other common colours of hydrogrossular stones, with pink and grey also known. Hydrogrossular stones are easily polished and make excellent pendants (polished or unpolished) and are sometimes used for other jewelry.
Seven stones from New Zealand, to Karen in Oklahoma.
TumbleStone 
Nice gesture John, a nice selection
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