Category: Calendar

The Introduction to this Calendar can be found here. 

The month of November in the 2026 TumbleStone Calendar features four breccia stones. A breccia stone is made up of angular non-rounded fragments, sometimes from different sources, cemented together in a fine-grained matrix. The matrix may be a mineral like quartz or calcite, or a material like silt or clay (in a petrified state). As University of Auckland Geology notes, if the fragments (also known as “clasts”) are rounded, the stone is instead called a conglomerate. Water is the most common cause of such rounding. Sometimes in a breccia, the fragments come from a single rock or rocks of the same type – these are called “monomictic” (“mictic” meaning “mixed”). Where the fragments comes from two or more rocks types, the stone is called “polymictic”. One of the main ways that breccia forms is when material accumulated on steep hill slopes or at the foot of cliffs consolidates into new rock under pressure and heat. Some breccias are produced by the fragmentation of rocks during faulting or tectonic stress, and volcanic breccias comprise small blocks of lava in an ash matrix, the product of a volcanic eruption. Two less common formation processes are when hydrothermal fluid fractures a rock mass, and when a meteor fractures rock at the site of an impact. Sandatlas provides a good detailed account of breccia and its formation.

Calendar Cover, 2026.

November.

November’s four breccia stones.

Stone One (top row, left, in Calendar) is a monomictic breccia from Ward Beach, Marlborough, found on 2 April 2025:

Stone One, November.

It’s likely to be limestone, a common rock in this area – it looks like the rock has fragmented under tectonic pressure and then heated water flowing through it has left something like quartz behind to fill the gaps.

Stone Two (top row, right, in Calendar), found on Gemstone Beach on 15 March 2025, is very unusual as it has a brecciated vein:

Stone Two, November.

This monomistic breccia stone is very similar to the one featuring in the Post “T is for a Type of Tiny Tectonic Breccia?” (not yet published), a green-hued stone with a vein containing tiny fragments of the same stone. As I note there, “Definitions of breccia usually refer to large-scale masses of rock, and they do not cover this form of brecciation WITHIN a small stone.”

Another green breccia is Stone Three (bottom row, left, in Calendar), found on Gemstone Beach on 27 March 2025:

Stone Three, November.

The green matrix is probably the mineral epidote which is usually described as “pistachio green”. The light-coloured fragments or clasts all look like they might be a fine-grained mudstone, again making this a monomictic breccia.

Stone Four (bottom row, right, in Calendar), found on Slope Point on 10 March 2025, is polymictic, its clasts coming from different sources:

Stone Four, November.

The fragments don’t stand out as clearly as in Stone Three but careful examination shows a range of them in terms of size, colour and make-up. Particularly attractive are the lightest coloured ones with tiny spots in them. These spots might be crystals or even tiny fragments – if the latter, this would mean that some of Stone Four’s clasts are themselves originally part of a different breccia.

For December’s hydrogrossular garnets, see this Post. 

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.

Calendar Cover, 2026.

September.

September’s Unidentified stones.

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

Stone One, September.

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

Stone Two, September.

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:

Stone Three, September.

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:

Stone Four, September.

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:

Stone Five, September.

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.

The Introduction to this Calendar can be found here. 

The month of August in the 2026 TumbleStone Calendar features six yellow stones of various hues. They come from five different South Island beaches. Yellow in a stone is often produced by the presence of iron oxide, which can also give rise to browns and reds and even blacks. Yellow is sometimes due specifically to the presence of hydrated iron oxide hydroxides, also known as limonite. Mindat notes that the most common form of limonite is goethite, but it can also include hematite, for example, and even some quartz and clays.

Calendar Cover, 2026.

August.

August’s yellow stones.

Stone One (top row, left, in the Calendar) comes from Ward Beach in Marlborough, found on 29 July 2025, the day on which I also found September’s unidentified Stone Four. It is a yellow stone with a white vein and dark markings which look like lines of dots:

Stone One, August.

The stone could be limestone, which is common on Ward Beach. Limestone is usually a biological sedimentary rock, forming from the accumulation of shell, coral, algal, and other organic debris – see Geology.com and “Selection of Tumbled Ward Beach Stones: Part 2 – Other Limestone Pebbles”. I am unsure what the white vein consists of as it does not have the usual density and brightness that quartz would have. The black lines are most likely dendrites which are are thin, branching crystals, often of some variety of manganese oxide (or iron), that grow over a surface of a rock. They are usually found in cracks or along bedding planes. See “D is for Dendrites” (the second part of this Post) and the second part of “Selection of Tumbled Ward Beach Stones: Part 3 – Stones With Veins; Stones With Dendrites”.

Stone Two (top row, centre, in the Calendar) is a hydrogrossular garnet collected from Gemstone Beach, Southland, on 3 August 2025:

Stone Two, August.

Hydrogrossular garnets come from dense rock masses, not crystals. The first ever identification of hydrogrossular garnet in the world was in 1943 by New Zealander Colin Hutton, from stones found in Nelson. Many fossickers visit Gemstone Beach to look for them as they are easily polished and make excellent pendants. 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 some hydrogrossular garnets, and some are a light grey. However, other minerals can get mixed in, as in the case of Stone Two where something like iron oxide has produced its yellow-orange patches. Stone Five (below) is also a hydrogrossular garnet and the month of December in this Calendar features five more hydrogrossular garnets.

Stone Three (top row, right, in the Calendar) comes from Bluecliffs Beach, to the west of Gemstone Beach along the Te Waewae Bay coast:

Stone Three, August.

I found Stone Three on 20 August 2025, one of only nine I collected that day – as you move west along this coast, the stones get bigger, so Bluecliffs Beach has mainly quite large ones. I mainly adopted a “photo fossick” approach with the larger stones, coming away with only a photograph of them. The smaller stones were much less common. Stone Three is probably an iron oxide-stained quartz, but it has a bright yellow-orange hue unevenly distributed through it, leaving interesting patterns.

On a beach near Slope Point at the very bottom of the South Island, I came across Stone Four (bottom row, left, in the Calendar) on 10 March 2025 – it’s yellow with some flecks of red:

Stone Four, August.

This was quite a surprise as I usually collect this type of stone on Seadown Beach, Kakanui, North Otago, nearly 300 kilometres north of Slope Point. Stone Six is such a find from Kakanui. What is special about these yellow-brown stones is that they contain lots of tiny fossils, most of them bryozoa. Bryozoa are one-celled animals which live in colonies. They have a partially calcified hard body wall, which is subject to the process of fossilisation. There are many species and many different types, including branching twig-like forms, lacy forms and fan-like forms. It is very difficult to see them with the naked eye – the close-up photos reveal the complexity of them. I am grateful to John Taylor, who lives in Scotland, for help in identifying this type of stone, who also suggested it was chalcedony (a form of cryptocrystalline quartz) – see “Bryozoan Fossils in Chalcedony, Kakanui’s Seadown Beach”. There is a little bit of clear or white chalcedony that can also be glimpsed in some of the veins in Stone Four. Slope Point beaches are usually dominated by rhyolite stones, with some nice petrified wood there too, but every now and then I come across a real surprise, like Stone Four.

Stone Five (bottom row, centre, in the Calendar), like Stone Two, is a Gemstone Beach hydrogrossular garnet, found on 12 August 2025:

Stone Five, August.

In Stone Five, the iron oxide (if that is the mineral providing the colour) is through all of the stone and ranges in hue from light yellow to dark red.

Stone Six (bottom row, right, in the Calendar), like Stone Four, contains bryozoan fossils in chalcedony, though it was found 300 kilometres away at Seadown Beach, Kakanui, on 25 August 2025:

Stone Six, August.

Compared to Stone Four, Stone Six has more brown in it, alongside the yellow.

For September’s set of “unidentified” stones, see this Post.