Category: Slope Point

“Sally” made a comment on my recent Post “Unidentified Fossil Stone from Slope Point Polished” that is very intriguing. I am grateful for her suggestion. There are some tiny shapes in this stone that have been very difficult to identify. Some of them look like long-stemmed mushrooms (as circled below).

The unpolished stone, wet.

The stone after polishing.

One suggestion is that the stone is fossilised forest floor, something that occurs in the Slope Point area. I had wondered at one point if they might be fossil sponge spicules. Sally commented as follows:

The tiny long-stemmed fungi resemble Rayleigh-Taylor instability. This concept is used to describe various fluid dynamical systems, including when a heavier fluid is suspended above a lighter fluid within a gravitational field. I wonder if it can approximate cooling lava as it forms solid rock. See this link for images of Rayleigh-Taylor simulations: https://computing.llnl.gov/projects/blast/rayleigh-taylor-instability. I’m going to guess this pebble is/was orbicular rhyolite, an extrusive igneous rock formed by silica-rich volcanic ash. I’d love to hear from a geologist about it. Very beautiful!

Wikipedia notes: The Rayleigh–Taylor instability… is an instability of an interface between two fluids of different densities which occurs when the lighter fluid is pushing the heavier fluid. Examples include the behaviour of water suspended above oil while under the influence of Earth’s gravity, and mushroom clouds like those from volcanic eruptions and atmospheric nuclear explosions. One publication illustrates the way the two fluids interact, over time and at a certain temperature, as follows:

The fourth and fifth stages here produce a shape very similar to the tiny “fossils” observed in my Slope Point find.

Sally suggested the stone could have started off as orbicular rhyolite – the very similar sphericular rhyolite is often found at Slope Point, though it is relatively rare.

Sally’s suggestion that the tiny long-stemmed fungi shapes could be due to Rayleigh-Taylor instability may or may not be correct, and it will be difficult to verify it. However, it is an intriguing hypothesis that is not out of the bounds of possibility.

I found this small stone on a Slope Point beach in September 2024. After photographing it and looking at the images closely, it appeared to have many tiny fossils of some kind in it. This is how it looked that day:

Intriguing small stone.

Other side of stone.

I have tried to identify the small shapes within the stone but have not yet been entirely satisifed with a solution. I recently tumble-polished the stone – the outcome was not as good as I had hoped but the shapes have been clarified significantly. They are amazing! A few of them look like tiny long-stemmed fungi. This is one side of the stone now:

I have been busy lately not only with tumble-polishing but with a small book that I am putting together with Chrissy Lampitt who writes the Tumble and Polish Blog. It’s a kind of our identification guide to Gemstone Beach stones, or at least some of them, and is likely to take some months to complete. So far we have collected photos and text relating to argillite (including banded and spotted varieties), trace fossils, thulite, rhyolite (including ignimbrite), and jasper (including poppy jasper). I’ve just starting looking through my photos for specimens of amygdaloidal stones.

The 50 “extra” finds.

The waves moving back down the beach.

I discovered on Tuesday that I had missed a bag of stones I had collected from Slope Point when doing the previous Post. So I had another 50 Slope Point stones to add to the original 85. Below are photos of 12 of them.

The first one is a light-coloured rhyolite with interesting spherical-like features in it:

This much darker rhyolite has interesting lines/bands:

The shapes of the tiny crystals in the next stone are fascinating:

More tiny fascinating crystals, this time in a small dark stone:

There’s a lot packed into this stone, lots of detail:

I’ve collected three or four stones like the next one from Slope Point before. I love the tiny bits in it, a diversity of types of crystals:

The crystals in this stone remind me of bursting fireworks in the sky:

The patterns in this stone are quite unusual:

Other side of stone.

The final four finds featured here:

Part 23 is entitled “Here is bigger than you can imagine: A Tectonically Stressed Find from Gemstone Beach and an Afternoon Earthquake”. An Index to this Series is here.

85 of my Slope Point finds.

Small petrified wood pebble, Slope Point.

Slope Point beauty.

Agate, Slope Point.

I drove the 90 minutes over to Slope Point this morning, the southernmost part of the South Island. I had also visited there two weeks ago. I took the chance to check out the new public toilets and information shelter at the tourist carpark. These photos were taken on my phone, often quickly because of the number of people around:

A busy tourist carpark at Slope Point.

The new Information Shelter.

People walking across the paddocks to Slope Point itself.

Part of the timeline in the Information Shelter.

Seven people are acknowledged here.

The new public toilets at the Slope Point tourist carpark – two cubicles.

The view from the tourist carpark to the beach I visited – it lies behind the headland indicated by the arrow.

There are always unusual stones to be found at Slope Point, very different from Gemstone Beach. I spent just over two hours on a beach there, arriving at high tide. Despite the beach being only about 250 metres long, there’s a lot of stones there. Again, the photos below were taken on my phone.

The beach I visited – the waves moving onto the beach…

The waves moving back down the beach.

Powerful waves crashing against the rocks at Slope Point.

Slope Point itself can be seen ahead in the distance.

Slope Point beach stones.

85 of my Slope Point finds.

The waves were powerful, the weather coolish but sunny. I had a productive fossick, and collected just over 130 stones. This Post features 22 stones taken from a group of 85, the first bags I emptied when I go back to my accommodation.

The first is a bright colourful stone that easily caught my eye on the beach:

Slope Point beauty.

I was pleased to find this small petrified wood pebble. A lot of Slope Point petrified wood is black but there are some really nice non-black pieces to be found there too. This stone has enough light brown in it to make it really interesting:

Small petrified wood pebble, Slope Point.

Another side of the pebble.

A third side of the pebble.

The next stone was a totally unexpected find. It appears to be a type of agate (chalcedony). I’ve not seen anything like it at Slope Point before (or anywhere else, for that matter):

Agate, Slope Point.

Another light-coloured stone, appearing to have a lot of quartz in it? On the beach, I could see lots of tiny features in it:

Another unusual stone, with intriguing shapes in it:

I picked up the next stone because of the interesting different-coloured patch in the middle of it:

Two stones with green in them – the first with a little white in it, the second with a lot of black:

When I picked up the next stone, I thought it was simply a quartz stone, with bits and pieces of quartz in it. More careful examination reveals that it is a breccia, made up of tiny fragments of different rocks:

There are a range of types of breccia stones that can be found at Slope Point. Here are other breccias I picked up:

Sometimes it can be difficult to distinguish between clasts (tiny fragments of rock) in breccia and crystals in volcanic stones, but I think the above five are all breccia.

Next are four of my finds that looked fairly regular in their composition, though the close-up photos often reveal unexpected details. Usually the tiny features are crystals:

Four stones that I think are likely to be rhyolite:

The next Post features more stones from this trip to Slope Point. An Index to this Series is here.

Looking towards where the track comes down to the beach.

My 90 finds from Slope Point today.

Very similar to a Kakanui bryozoan fossil stone.

Fragment of a jasper.

Slope Point petrified wood.

I drove 90 minutes to Slope Point yesterday, in the company of Chrissy. I always try to visit there at least a couple of times each trip south. We arrived just after noon and just before high tide. The sea was reasonably calm despite a strong swell being apparent. We spent about 2½ hours on a small Slope Point beach, the one featured in this 2023 Post. Then it was a slow climb back up the steep track to the car with our finds. We paused partway for me to take a side-trip to a small cove located down an even steeper slope. A large sea lion had somehow made its way up to that point of the track and had hunkered down in the long grass. It poked its head up and we carefully skirted around it.

The small Slope Point beach we visited.

Chrissy on the way down to the beach. Slope Point itself, where the tourists go, is straight ahead, just over her head in the middle background.

Chrissy’s phone photo of me on the way down to the beach, Slope Point.

Looking towards where the track comes down to the beach.

Chrissy’s phone photo of the sea lion that was located half way up the track, in long grass near a large flax bush. Slope Point.

Chrissy’s phone photo of me down in the small cove.

My 90 finds from Slope Point today.

The beach is only about 250 metres long, but there’s a lot of stones there. The waves have a lot of energy so care has to be taken to keep your boots dry. On Gemstone Beach, I tend to walk along slowly until a stone catches my eye. On this Slope Point beach, a more effective strategy is to take a step and bend down and look carefully at the stones before taking another step. This is because, as Jocelyn Thornton notes in her “Gemstones” booklet about Slope Beach stones: “At first glance they appear dark, but closer examination reveals a multitude of subtle colours and patterns” (see page 35 here).

Slope Point stones.

More Slope Point stones.

Slope Point stones.

We didn’t find any spherulitic rhyolite or fossil punga – see the first two stones in “Some More Recently Polished Stones from Slope Point and Kakanui” – and we didn’t find any of the brown petrified wood that sometimes has agate in it – see “January 2022, Stone of the Day #10”. I collected 90 stones that caught my eye for some reason (colour, lines, patterns). I thought it was a mediocre fossick until I looked at the stones more closely after getting back to Riverton. Many of them are fascinating! Eighteen of my finds are featured below.

The first one was the most surprising. A small stone that stood out due to its pale yellow clay-like colour, it appears very similar to the bryozoan fossil stones I have found previously at Kakanui. I have not seen anything like this anywhere apart from at Kakanui and its presence at Slope Point came as a complete and unexpected surprise.

Very similar to a Kakanui bryozoan fossil stone.

Another side of the stone.

Another side of the stone.

Another side of the stone.

I suspect the tiny features in the stone are fossils of some kind, some of them being bryzoan.

Another amazing find is this tiny jasper fragment. I spotted its red hue and decided to pick it up for a closer look despite it being so small. I could see enough to let me know it was going to be worth putting in my bag so I could take a closer look via my camera back at the crib.

Fragment of a jasper.

Another side of the jasper fragment.

The next find is a good example of the kind of Slope Point stone that Jocelyn Thornton refers to as containing a “multitude of subtle colours and patterns”. My guess is that it’s a kind of rhyolite:

Other side of stone.

The bright orange in this sedimentary stone caught my eye:

It might be a little soft to tumble polish but I thought I might give it a go. Another one that might be too soft for tumbling, but its pink colour and contrasting textures are interesting:

This one appears to be a breccia, small fragments from different stones cemented together in a fine grained matrix:

A different breccia, darker in colour and slightly larger fragments:

A couple of light brown stones with black spots:

The red in this stone is subtly different from the usual jasper red. It appears to be igneous:

Two lighter coloured stones with complex structures, again good examples of “subtle colours and patterns”:

Two of the darker coloured stones that caught my eye:

The fine white lines in this stone reminded me of lightning:

Two small finds, the first being a quartzy one, the second a granite pebble with well-defined white crystals, probably feldspar:

A type of quartz or quartzite??

Small granite pebble.

Finally, a piece of black petrified wood I brought up from the small cove. When wet, the grain of the wood can’t be seen so this photo is of the dry stone:

Slope Point petrified wood.

We had aching muscles by the time we finished our walk back up the hill to the car. It was then another 90 minute drive back to Riverton, and then Chrissy had another 30 minutes or more back to her home. But it turned out to be well worth it.

The next Post in this Series is “A Stormy Sea and Swollen Streams at Gemstone Beach“. An Index to this Series is here.

The beach as we arrived. Photo by Chrissy.

Chrissy and I travelled to Slope Point this morning, a 90 minute drive from my base in Riverton Aparima. Slope Point stones are very different from those to be found on Gemstone Beach, many more of them being of volcanic origin. We visited one of the beaches there for about two and a half hours, leaving just as a heavy downpour of rain hit the region.

Slope Point is the southernmost tip of the South Island, and a handful of its beaches have long been visited by stone fossickers. Recently, landowners have restricted the beaches that can be accessed. Some of the Slope Point stones have arisen from Jurassic Era volcanic activity and debris flows. Petrified wood, fossil tree fern, colourful rhyolites and interesting breccia can be found there. Jocelyn Thornton’s “Gemstones” has an informative page on Slope Point stones (page 35). However, the steep slopes and distance from good roads mean that the fossicker has to be determined and prepared to carry heavy finds some distance back up-hill. Rock and Mineral Club expeditions sometimes head this way. For example, the Southland Geological and Lapidary Club has planned a trip there on Sunday.

When Chrissy and I reached the beach, the tide was low and the sea was very calm. The beach is a small one, maybe only two hundred metres long, with a rock platform at one end and high cliffs with outcrops of conglomerate strata at the other. Today there was a bit more sand on the southern part of the beach than is often the case, but there were still plenty of stones to search through.

John on the walk down to the beach. Slope Point is in the far distance. Photo by Chrissy.

The beach as we arrived. Photo by Chrissy.

The rock platform at the south end of the beach. Photo by Chrissy.

Large conglomerate rocks can be found on the beach, coming from the cliffs behind. Photo by Chrissy.

The beach when we left. Photo by Chrissy.

Compared to Gemstone Beach, the stones tend to be more knocked around, and many otherwise attractive specimens have chunks out of them, scratches across their surface, or have small holes in them. These pose more of a challenge to the tumble polisher. This morning, spending time looking carefully among the dry stones up the beach proved most productive – for some reason, we found fewer stones of interest at the waves’ edge. I collected about 130 to take home.

I didn’t find any of the sought-after petrified wood, tree fern or chrysanthemum rhyolite this morning (see this Post and this Post for examples). But this first stone is an example of the surprising beauty that can sometimes be found in the Slope Point area:

Intriguing small stone.

Other side of stone.

A Slope Point rhyolite that contains some circular features that can sometimes be found here:

Slope Point rhyolite.

Another side of the Slope Point rhyolite.

A third side of the Slope Point rhyolite.

A very dark stone, with some circular features, which I think is also a rhyolite:

Rhyolite?

Other side of stone.

Probably a volcanic breccia:

Volcanic breccia?

Other side of volcanic breccia.

This stone is probably rhyolite but it seems to have some tiny angular fragments in it too:

Rhyolite?

Other side of stone.

Sometimes it can be difficult to decide whether the features in a stone are crystals or fragments of other stones, as in this small pebble:

A similar shaped pebble:

Two lighter-coloured stones, also with intriguing tiny markings:

Slope Point stone.

Three more of the lighter-coloured finds from this morning:

And six of the darker-coloured finds:

Rhyolite.

Flow banded rhyolite.

Flow banded rhyolite.

Rhyolite.

Slope Point stone.

Slope Point stone.

The cliffs along the north of this beach consists of a strata of conglomerate rock. There are lots of rounded stones embedded there, many of them larger than a fist. It is also possible to find conglomerate stones on the beach, made up of small rounded fragments, like this one, which also has an interesting “other” side:

Small conglomerate stone, Slope Point.

Other side of small conglomerate stone.

I try to collect reasonably smooth stones – the chance of a successful tumble polish is enhanced by this. However, despite its chunky character (hollows and jagged ridges), I couldn’t leave this one behind. I will need to use more coarse grit in the tumbler than usual for it.

Chunky Slope Point stone.

Other side of stone.

I was very surprised to find a nice specimen of yellow quartzite. It is much more common along the North Otago and Canterbury coastline:

Yellow quartzite, Slope Point.

On the way back home, I stopped briefly to take a look at a new Information Kiosk at the Slope Point tourist carpark – it has great information on the history of the area. But the wind and rain made it unpleasant to linger. It looked like a toilet block is also being built there.

The next Post in this Series features another fossick on Gemstone Beach, highlighting some colourful finds. The Index to the Posts in this Series can be found here.