TumbleStone Calendar 2025: September and October

The 2025 TumbleStone Calendar features beach stones collected during my two South Island fossicking trips in 2024. Details about the stones shown in the months of January and February are here, in March and April here, in May and June here, and in July and August here.

The first month in this Post, the month of September, is another featuring Southland’s Gemstone Beach (Southland). October takes us back to Ward Beach (Marlborough), first encountered in the month of May. The stones in this Calendar were photographed in the rough while wet, held in my hand in bright sunlight. Often the photos reveal much more about the stones than I initially noticed when I picked them up. Also note that my identifications of stone types are generally tentative.

SEPTEMBER – GEMSTONE BEACH

This is what a British newspaper, “The Guardian”, wrote in September 2024, in a long and interesting article about Gemstone Beach and its people: “At a distance, the stones look like any others found along New Zealand’s rugged Southland coast, but here, at Orepuki – or Gemstone Beach – a closer look reveals a bed of riches. Jasper, hydro-grossular garnet in pinks, greens and yellows, patterned fossilised worm-trails, spotted argillite, frosty white quartz, speckled granites, pink-flecked rhodonite and – in rare cases – the unmistakable blue of sapphire, colour the low-tide line.” Such articles tend to emphasise the “precious gemstones” to be found on Gemstone Beach but in reality the stones effectively have no monetary value. Maybe some of the colourful ones and some of the hydrogrossular garnets can be polished and made into low-cost jewelry, and maybe a collector might pay a little for one of the beach’s rare low-quality sapphires. But the real “treasures” to be found on Gemstone Beach are the gorgeous colourful “ordinary” stones that are remarkable for their natural beauty. You can find stones like these on many New Zealand beaches, but they seem to be more numerous and more concentrated at Gemstone Beach and the nearby coast of Te Waewae Bay. The month of September in the 2025 TumbleStone Calendar features four of Gemstone Beach’s treasures collected by me in 2024. The beach scene was captured on 21 March during my final fossick there for my first trip for 2024, though it does not feature in the Blog Post for that day.

September’s Stone 1 is a small hydrogrossular garnet, found on 27 February, though it is an unusual black and white colour for a garnet.

Gemstone Beach is particularly well known for its hydrogrossular garnets. These stones usually feel waxy and they shine brightly when wet, outshining even quartz. Hydrogrossular garnet is one of 13 minerals first described from New Zealand and accepted as valid by the International Mineralogical Association. There is an introduction to hydrogrossular garnets, along with nine specimens, in “First Identified in New Zealand in 1943 – Revisiting the Hydrogrossular Garnets of Gemstone Beach”. A lot more detail and many more specimens can be found on the TumbleStone Two page about Hydrogrossular Garnet.

Gemstone Beach’s Stone 2 for September is an unknown one to me. It was the areas of colour against a dark background that caught my eye on the beach on 25 September.

Its texture kind of reminds me of schist, because of its relatively coarse grain, with some added colour from a pinkish mineral. But I don’t know enough about schist for sure or to say much more. See University of Auckland Geology for a description of schist as a metamorphic rock.

Stone 3 for the month of September is another epidote. April’s Stone 2 was a type of orbicular epidote, I suggested. September’s Stone 3 has a more intense shade of green to it, brought out by the small patches of white and light grey.

Stone 4 is the third of three poppy jaspers to appear in the Calendar, the other two being January’s Stone 3, with larger orbs, and July’s Stone 4, with smaller orbs. Again hematite is present in the stone, adding to the intensity of the red.

All of the poppy jaspers I have found on Gemstone Beach have been small and have often been chipped. None have been bigger than three centimetres long, usually being even smaller. Not many of them can be tumble polished successfully due to their rough condition.

OCTOBER – WARD BEACH

Ward Beach in Marlborough features in three “Geotrips”. GeoTrips are guides to rock outcrops, geological displays or landforms that can be visited and explored in New Zealand. They have been compiled by GNS Science with the assistance of geologists and knowledgeable enthusiasts. Useful background information is provided, along with photos, maps, and directions how to get there. The first Geotrip to Ward Beach is entitled “Uplift at Ward Beach”. During the 14 November 2016 Kaikōura Earthquake, this part of the coastline was uplifted around 2.2 to 2.6 metres. “The change in ground level at Ward Beach has forced the Flaxbourne River to abandon its estuary and incise through the former estuary bed and gravel beach deposits, exposing more of the bedrock beneath.” The first two photos below show the uplift.

The second Geotrip takes readers to the Ward Beach boulders, 800 metres from the carpark (best visited at low tide). The third and fourth photo above illustrate this Geotrip. “These brown spherical rocks are concretions within Late Cretaceous (more than 65 million years ago) marine sediments… They consist of dolomite (calcium magnesium carbonate) that formed over several million years within a mudstone… Concretions usually start around a piece of wood, fossil or a shell and grow radially outwards by the precipitation of mineral cement.” Chancet Rock Reserve, the subject of the third Ward Beach Geotrip, is important because there, 1,500 metres north of the carpark, is an accessible outcrop where you can see the K-Pg boundary layer (formerly known as the K-T boundary) – see the fifth and sixth photos above. “The Cretaceous-Paleogene boundary was identified and confirmed by the presence of the ‘iridium anomaly’ with tens of times the normal concentration of iridium (a very rare metal) in a thin clay layer. This layer has been recognised worldwide and marks the end of the Age of the Dinosaurs, caused by a devastating asteroid impact that struck part of where Mexico’s Yucatan Peninsula is today.”

The month of October in the TumbleStone 2025 Calendar features four Ward Beach stones. I found all four stones on the same day, on 2 October, during a two hour fossick. The next day I caught the Cook Strait ferry on my way home.

Stone 1 is limestone with dark trace fossils through it.

On page 31 of “Gemstones”, Jocelyn Thornton has two specimens of “grey limestone with bands of worm trails like rows of arrowheads”. These can be found along the Marlborough coast and are common on Ward Beach. But there is a great diversity of these, with different trace fossil shapes, as can be seen in this Post. On the beach, when dry, these stones are dull and a cloudy white (see photos below). You have to look close to see anything in them and even then the details are not disclosed. You need to see them wet to discern their traces better.

Limestone is relatively soft and won’t stand up to the usual tumble-polishing process. Simply tumbling them for a couple of days in fine grit keeps them looking clear, even when dry.

October’s Stone 2 is a small jasper found on Ward Beach.

It is brecciated and has a large quartz vein at the top. Jocelyn Thornton has a number of examples of New Zealand jasper on pages 17 and 18 of “Gemstones”.

Stone 3 is, I think, what is called a magpie agate. Its black and white colour is what is shared with the magpie bird.

The black is likely to be flint and the white will be chalcedony, also known as agate. Chalcedony is a cryptocrystalline form of silica, which means that its crystals are less than 0.001 mm in size, too tiny to see even using a hand lens.

Stone 4 is a brecciated yellow jasper. Sometimes such a stone is called a storm jasper. It appears to have some quartz in it as well.

Miami Mining notes that the yellow colour is due to iron oxide: “Yellow jasper is known for its bright and bold colors, which are caused by the presence of iron oxide (hematite) within the gemstone. The amount and distribution of hematite within the gemstone can vary, resulting in a range of colors from pale yellow to deep orange and red.” Craftstones argues along similar lines, with an addition: “The presence of iron oxide (the mineral responsible for its colouring) pigments the compound [jasper], resulting in its distinctive colouring and patterns across the surface of the stone. This is very similar to the process in which red jasper is pigmented, however the iron [oxide] is exposed to significantly higher temperatures to achieve a rich yellow.”

The months of November (Seadown Beach, Kakanui) and December (Gemstone Beach) in the 2025 TumbleStone Calendar are featured in the next Post. These 2025 Calendars are for sale, with postage within New Zealand included, for $30 non-rural, $35 rural. Contact me at john.tumblestone@gmail.com.