TumbleStone Calendar 2026: September – Unidentified

The Introduction to this Calendar can be found here. 

The month of September in the 2026 TumbleStone Calendar features five “unidentified” stones. Sometimes it is very easy to identify a stone as it will clearly fit into a particular type. I am very familiar with a few beaches in the South Island, having spent a lot of time on them and having spent time finding out about their stones – that helps a lot. But it is not unusual to find a stone that defies easy identification. There is such a diversity on some beaches that identification can be a real challenge for the majority of my finds. And yet it is a stone’s visual interest that attracts me, even if I don’t know what it is. For the month of September, I chose five very interesting looking stones that I cannot identify with any certainty, if at all.

I found Stone One (top row, left, in the Calendar) on Gemstone Beach on 3 March 2025:

This is a gorgeous stone with lots of interesting features, swirls, veins, lined inclusions. There’s a lot going on in it. The lighter coloured material could be quartz or quartzite with iron oxide providing the colour. I’ve not seen anything like it before.

Stone Two (top row, right, in the Calendar) comes from Slope Point, the southernmost tip of the South Island. I collected it from a beach near there on 10 March 2025: xx

There are some similarities with Stone One, with the swirls, for example, but the colour is quite different and there are interesting white lines in it that could be chalcedony. I suspect the stone is rhyolite but I can’t be sure.

Stone Three (bottom row, left, in the Calendar) is another Gemstone Beach find, this time from 19 March 2025:

I am fascinated by the fuzzy light green material which I suspect is epidote. The white is likely to be quartz, but I don’t know what the stone overall would be called.

I found Stone Four (bottom row, centre, in the Calendar) on Ward Beach, Marlborough, on on 29 July 2025, the same day I found August’s yellow Stone One:

At the time, I thought it could be either a breccia (a stone made up of rock fragments in a matrix) or a stone containing pieces of shell (or fossilised shell). Whatever it is, I like the texture of the white fragments, seemingly made up of long thin rods. There is some similarity to the long thin pieces in another Ward Beach find which has been suggested to be a fossil oyster.

Stone Five (bottom row, right, in the Calendar) is another Slope Point stone, found on 24 March 2025, a very colourful one which easily caught my eye on the beach:

It kind of looks like a breccia, with angular fragments from a number of different rock types making it up. However, the orange colour in it seems to be present across a number of those fragments, undermining the idea of their different origins.

For October’s Kakanui quartzites, see this Post.