August 2025 Stone Collecting Trip – Part 7, A Rhodonite Find on Gemstone Beach, Wednesday 6 August

Gemstone Beach seagulls.

This afternoon I spent just over two hours on Gemstone Beach. I arrived at 2.20pm, two hours before low tide. It was 13 degrees throughout the fossick, with a strong breeze. I chatted to a couple from Arrowtown as I left, identifying three or four of the handful of stones they had found.

Gemstone Beach this afternoon. Looking west. A small group near the mouth of the Taunoa Stream.

Looking east from 100 metres east of the Taunoa Stream.

Gemstone Beach stones.

On the way back, the beach in front of the carpark, viewed from just west of the Taunoa Stream.

Seagulls over the breakers on Gemstone Beach.

Gemstone Beach seagulls.

The hydrogrossular garnets I found today were mainly small and, as with the previous fossick, I spotted very few trace fossil stones. I did find one small poppy jasper and the occasional interesting other kind of stone. Twelve of this afternoon’s finds are featured below.

Gemstone Beach stones.

More Gemstone Beach stones.

Today’s finds.

The largest stone I collected today is this rhodonite. Rhodonite is primarily composed of manganese silicate, its colour varying from light pink to deep red. It is similar in colour to thulite but often features black markings caused by manganese oxides:

Large rhodonite stone.

Other side of rhodonite stone.

Another glassy stone that has been suggested to me is chromite in quartz, two also having been found yesterday:

Chromium in quartz?

Holding the stone up to light.

A black and white stone where I suspect the white material could be hydrogrossular garnet, kind of similar to one I found on Sunday:

I found two small poppy jaspers, the first having a little green epidote in it:

Small poppy jasper with epidote.

Other side of stone.

Two finds with different types of brecciation (re-cemented fragmentation), the first the result of tectonic pressures on the whole stone, the second being limited to a vein:

Brecciated argillite.

Brecciated vein.

Next are the two largest of my hydrogrossular garnet finds – the first is partly transparent, the second is opaque and very waxy (so that water beads off it quickly):

Partly transparent ydrogrossular garnet.

Held up to the light.

Opaque hydrogrossular garnet.

Water moves off the waxy surface.

And now a couple of green-hued stones. The first is what is said to be the typical pistachio-green hue of epidote (though epidote causes a range of greens):

Probably green epidote.

The second is perhaps a form of spotted argillite (Stones Gn2 to Gn31 in this Post are examples of spotted argillite):

A type of spotted argillite?

A small banded argillite, a good example of an indurated banded mudstone:

Banded argillite.

Finally, what may be a quartzite specimen:

The next Post in this Series, “A Sense of Wonder: Poppy Jaspers and Exquisite Breccias”, covers my fifth fossick so far at Gemstone Beach this trip. An Index to the Series is here.

Author: tumblestoneblog

Retired Academic, male, living in the New Zealand countryside near Whanganui with his wife as well as Jasper the dog, Fluffy the cat, Dancer and Penny, the horses, and a shed half-full of stones. Email john.tumblestone@gmail.com. View all posts by tumblestoneblog