August 2025 Stone Collecting Trip – Part 11, Puffer Jacket and Woollen Hat and Scarf: A Winter Morning Fossick on Gemstone Beach, Thursday 14 August

This morning’s two and a half hours fossick began at low tide. It was another cool sunny day without wind, very comfortable for stone hunting as I was wearing a puffer jacket and woollen hat and scarf. I noted the presence of four other serious fossickers there at different times, plus some passing motorists. I spent part of my fossick looking at the stones which had accumulated at the foot of the cliffs which back the beach. When I departed at 12.15pm, there were eight other vehicles in the carpark.

The first of today’s featured finds caught my eye because of the small circular features in it:

I like the texture of this stone:

There are some interesting tiny veins in this small find:

Two different poppy jaspers, with two sides of the second one shown:

An amygdaloidal stone, a stone with many tiny vesicles (gas holes) that have been infilled with minerals:

An argillite stone with dark trace fossils in it:

Trace fossils are not fossils of an animal but are fossils of the traces they leave behind. “Trace fossils are what is left of the activity of some ancient critter”, writes retired kiwi geologist Brian Ricketts in his blog “Geological Digressions”. That activity includes burrowing, moving, excreting, fighting and feeding.

Finally, two hydrogrossular garnet finds:

As I note in a detailed Post on them, hydrogrossular garnets are not like the garnets we know as precious gems – they come from dense rock masses, not crystals. Technically, hydrogrossular garnets are a calcium aluminium garnet with hydroxide partially replacing the silica found in other garnets. The first ever identification of hydrogrossular garnet in the world was in 1943 by Colin Hutton, from stones found in Nelson, and it is the most widely spread of the 13 minerals first described from New Zealand. More details can be found in “First Identified in New Zealand in 1943 – Revisiting the Hydrogrossular Garnets of Gemstone Beach, February 2023”.

The evening after this fossick I drove to Invercargill to attend the monthly meeting of the Southland Geological and Lapidary Club. Around 15 or 16 others were there. Guest speaker was Lloyd Esler, a well-known Southland historian and teacher. He handed around about 20 rocks, fossils and artefacts, and talked about them. One was a ventifact, a stone shaped by wind-driven sand. Another was fulgurite, created when sand gets fused together by a lightning strike. From Gemstone Beach, there was a trace fossil stone and some vivianite, a blue mineral associated with decaying organic matter – this was from the peat layer in the Gemstone Beach cliffs. Then there was a container of volcanic ash, very fine and abrasive. Lloyd mentioned how flying through a volcanic cloud had once shut down a passenger airplane’s engines. I remembered this incident from my viewing of the excellent air crash investigation documentaries so I hunted it down on YouTube. Here is the episode about that 1982 747 flight:

The next Post in this Series covers two fossicks on a Te Waewae Bay beach at Papatotara. An Index to the Series is here.