Nine South Island Tumble Stones for Germany

Kakanui beach stones.

My wife has gone to Germany to visit family, after a long period of absence due to the pandemic. I sent nine stones with her as gifts for members of her family, little bits of New Zealand traveling to a foreign land.

The first stone is a gorgeous brecciated jasper from Kakanui (North Otago), that was Stone of the Day #8 in January this year.

Jasper is a form of chalcedony. Chalcedony is cryptocrystalline quartz, where “cryptocrystalline” means a rock texture made up of such tiny crystals that its crystalline nature is only vaguely revealed even microscopically. The most common red colour of jasper comes from the presence of iron. In a brecciated jasper, the original jasper stone is fragmented by pressure and infilled with quartz. It’s like looking down on islands of red drifting in a white sea. This particular stone is one of the top two or three in quality that I have found. Some background information on Kakanui can be found in this Post.

The second stone is banded ignimbrite, found at Gemstone Beach, Orepuki, in Southland. Stones like this caught my attention early on when I started tumble polishing because of their banding and tiny infilled gas pockets. They look like glimpses of deep space.

Ignimbrite is a form of the volcanic rock rhyolite and originates as the deposit of a pyroclastic flow, a hot suspension of particles and gases flowing explosively and rapidly from a volcano. A little more on these stones can be found in this Post. An account of Gemstone Beach can be found in this Post.

Stone Three is unique in my collection, found at Slope Point at the southernmost point of the South Island.

I go to Slope Point to find colourful rhyolite stones but occasionally find different interesting ones (see this Post for some background on Slope Point). This stone caught my eye because of the fine tracery of black lines across the gray. I first thought it might be sedimentary, the lines being laid down as part of accumulating layers of sediment at the bottom of the sea. But then I saw that the lines often run at different angles to each other… It’s a bit of a mystery how they would have formed.

The fourth stone is a quartzite from Birdlings Flat, near Christchurch in Canterbury.

Birdlings Flat is perhaps the most famous beach for fossickers in New Zealand. See this Post for more information about it. Quartzite is a metamorphosed sandstone. It starts off as quartz sand. The intense heat and pressure of metamorphism causes the quartz grains to compact and become tightly intergrown with each other, resulting in a very hard and dense rock. Minerals can flow through the hot liquid during this process, adding colour and patterns. Up close, you can often see tiny clear quartz crystals in these stones as well. This kind of quartzite, with yellow in it (almost orange in this stone), has long been one of my favourite stones and it tumble polishes well (see this Post for yellow quartzites I found at Birdlings Flat in 2016 when I first starting collecting and polishing, and see the entry for Wednesday 26 May 2021 in this Post for an idea of the variations in colour of such quartzites, those these four are from Kakanui).

Stone Five is a small jasper stone from Gemstone Beach in Southland.

Its colours are more muted and delicate than many jaspers but it has interesting patterns on it. See the comments on Stone one above for some information on jasper. An account of Gemstone Beach can be found in this Post.

The sixth stone is argillite and contains a number of trace fossils. I found it on Gemstone Beach in Southland. Trace fossils, also called ichno-fossils, are the fossilised marks, tracks, burrows and deposits of animals.

About 250 million years ago, in the Permian Era, these traces were left in ocean-bottom sediments by the activities of ancient worms and other small animals. Argillite is a hardened partly-recrystallised mudstone formed from ocean floor sediments. In the south of New Zealand, the ocean floor was uplifted by massive geological forces and the argillite was faulted and fragmented. Some of these fragments were carried out of eastern Fiordland by streams into the Waiau River then into Foveaux Strait, some eventually washing up on Gemstone Beach. There is a great diversity of trace shapes to be found in these stones, along with variations in size and colour. Stone six is unusual because of the number and diversity of trace fossils it contains. An account of Gemstone Beach can be found in this Post.

Stone Seven is a deceptively plain stone, being white and with few other features. It is a hydrogrossular garnet and it too comes from Gemstone Beach in Southland.

Technically, hydrogrossular garnets are a calcium aluminium garnet with hydroxide partially replacing the silica found in other garnets (this Post explains further). The first ever identification of hydrogrossular garnet in the world was in 1943 from New Zealand, one of 13 minerals first described from New Zealand. 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. 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 – it is the most sought stone on Gemstone Beach, the only place in the lower South Island that it can be found (it can also be found near the northern part of the South Island). I always keep an eye out for it. It is reported that the indigenous people of New Zealand, the Māori, used hydrogrossular rocks as hammer-stones because of their hardness.

The eighth stone is, like Stone Four, a quartzite, though it is from Kakanui in North Otago, not Birdlings Flat in mid-Canterbury. And, unlike Stone Four, it has red in it.

The account of Stone Four describes how quartzite originates with quartz sand that then has minerals added to it to form its colours as it melts and cools. Red quartzite is less common than yellow in the Kakanui area. The Kakanui beach on which I found this stone is a stretch of maybe 1500 metres. It is unique in the area – all the other beaches I have visited to the south and north of it do not have such a diversity of interesting and smooth stones. I try to visit it three or four times a year, staying at nearby accommodation for a couple of days so I can make four or five fossicking trips to it each time. Some background information on Kakanui can be found in this Post.

Stone Nine also comes from Kakanui, a small dark red jasper with quartz veins. Often, jasper can be very difficult to tumble polish successfully but this stone has polished quite well.

Some information on jasper is given for Stone One above. This Post records one of my fossicks at Kakanui earlier this year. This Post contains examples of other jasper stones found at Kakanui.