Month: August 2024

This Series features tumbled stones from Ward Beach, Marlborough. These are part of a selection that I am leaving with Ronnie and Ian who run the Flaxbourne Motels in Ward. The first four Parts in this Series highlighted stones that are softer than usual for the polish tumbler. Part 1 dealt with trace fossil limestone pebbles, Part 2 with other kinds of limestone pebbles, Part 3 with veined stones as well as stones with dendrites, and Part 4 with stones that are a mix of soft and hard material. This final Part in the Series presents a number of hard Ward Beach, the more usual and better suited material for tumble polishing.

I usually look to collect the softer stones from Ward Beach, especially the trace fossils which I find particularly intriguing. Sometimes, a harder stone crops up, though not very often. That may be because I am not looking out for them. During my most recent visit, I deliberately looked for stones that I normally don’t focus on – see towards the end of this Post. Some of the following were found at that time.

The most spectacular of these stones is this small one, probably a form of chalcedony but I am unsure. The detail inside it is amazing:

Another interesting mainly brown-coloured stone but with a striking dash of white:

This one is an interesting mix of muted colours, caused by different minerals within it:

I particularly looked for red jasper stones in March this year and found a few, many of which weren’t very interesting. These were the two best, the first one also having hematite in it (a type of iron oxide) – see the second entry in this Post for details on hematite jasper. The second has a white quartz vein with tiny fragments of jasper in it:

A few stones that initially looked like limestone but turned out to be much harder:

The previous two stones are igneous, most likely from a volcanic source – the light and dark crystals that grew while the molten rock cooled can be seen in them. The final three stones are also volcanic in origin:

This is the final Post in this Series. The first Post can be found here.

I am giving some tumbled Ward Beach stones to Ronnie and Ian who run the Flaxbourne Motels in Ward, Marlborough. This Series features a selection of these stones. Part 1 dealt with trace fossil limestone pebbles, Part 2 with other kinds of limestone pebbles, and Part 3 with veined stones as well as stones with dendrites. This Part presents Ward Beach stones that contain a mix of soft and hard material. These are difficult for a tumble polisher as the soft material wears away much quicker in the tumble barrel than does the hard material. So such stones have to be treated with some care.

In a Post reporting on my most recent fossicking visit to Ward Beach in March this year, I noted how the rocks to the south of the carpark appear to be limestone with darker flint patches and nodules. Flint is often to be found in association with limestone. Flint is a sedimentary cryptocrystalline form of quartz. In other words, the quartz has been put under pressure and heat to the extent that the crystals become too small to be recognised and separately distinguished even under an ordinary microscope. The following are stones that appear to have hard (flint) and soft (limestone) material in them, the hard material being more resistant to erosion.

The next set of stones also appears to be a mix of soft and hard material but in a more complex way and not always a mix of limestone and flint:

The final Post in this Series features Ward Beach stones that are hard in nature, the usual kind for tumble polishing.

This Series features tumbled stones from Ward Beach, Marlborough. These are part of a selection that I am leaving with Ronnie and Ian who run the Flaxbourne Motels in Ward. Part 1 in the Series dealt with trace fossil limestone pebbles and Part 2 with other kinds of limestone pebbles. This Part presents a number of Ward Beach stones with noticeable veins as well as some stones with dendrites.

A “vein” is an infilled crack. When rock comes under pressure and stress, it fractures, and cracks of different sizes open up. This allows hydrothermal fluids (such as super-heated water), carrying dissolved minerals, to enter the gaps in the rock. Over time, the dissolved minerals precipitate out of the hot water. Crystals, such as quartz, grow within the cracks and fill them. Often, as the stresses on the rock change their orientation over time, veins will crosscut and even overlie each other. For useful information on this process, see the section on “Veins” in Geology Fundamentals and the entry on “Veins (Geology)” in Wikipedia.

Some tumbled Ward Beach stones with significant veins – all of these stones are relatively soft, most of them being limestone:

Some stones have cross-angled veins and others are quite fragmented so that the veins are quite complex:

“Dendrites” are quite a different phenomenon from veins. The word “dendrite” is from the Greek word for “tree”, referring to its branching. In geology, dendrites are thin, branching crystals, often of some variety of manganese oxide (or iron), that grow over a surface in a rock or mineral – see Mindat.org. They are found in cracks or along bedding planes. They often form lines which branch out across a stone. Dendrites are often given as examples of “pseudofossils”, natural objects that may be mistaken for fossils (of a plant leaf, for example) – see the section on “Dendrites and Manganese Forms” in Pseudofossils.

Some Ward Beach stones with dendrites:

The next Post in this Series features Ward Beach stones containing a mix of soft and hard material, especially limestone and flint.

This Series features tumbled stones from Ward Beach, Marlborough. These are part of a selection that I am leaving with Ronnie and Ian who run the Flaxbourne Motels in Ward. Ward Beach is six kilometres off the main road east from the small village of Ward, 82 kilometres north of Kaikoura and 45 kilometres south of Blenheim. Part 1 in the Series dealt with trace fossil limestone pebbles and this Part deals with other kinds of limestone pebbles.

Most stones look dull when you see them dry on the beach. Surface weathering, dust and mud tend to cloud their appearance. If you look at them wet, however, their colours and patterns usually come alive. Tumble polishing produces a stone that is smooth and shiny, with its colours and patterns permanently on view. Many of the stones on Ward Beach derive from the local limestone. Limestone is too soft for the normal tumbling process, quickly wearing away in the tumbling barrel. However, after some recent experimenting, I realised that a short tumble of a handful of days in fine grit would remove the cloudy surface and leave a nice smooth waxy-feeling stone. This form of tumbling doesn’t give such a stone a high polish, but its surface is permanently clear, showing its colours, veins and patterns clearly.

Limestone usually consists mainly of the bones and shells of tiny marine fossils made of calcium carbonate (see Te Ara Encyclopedia of NZ). Rocks with more than 50% calcium carbonate are considered to be limestone. University of Auckland Geology points out that there are many different types of limestone formed through a variety of processes. Some form from the cementation of sand or mud by calcite and these can have the appearance of sandstone or mudstone. My ability to accurately identify beach stones is limited. So I can’t be sure that all of the following stones are indeed limestone. I am fairly sure that at least some of them are, partly because of the waxy feeling they have after tumbling.

The first four stones are light coloured, mainly light gray:

However, there seem to be a number of “pastel shades” of limestone pebbles on Ward Beach as well:

Some limestone pebbles have thin veins running through them:

Some have a pattern of lighter and/or darker colours:

Some limestone pebbles can have complex and/or symmetrical patterning:

The second and fourth stone in the four above have not come out of the tumbling as smooth and clear as I had hoped. Not all stones do.

The next Post in this Series features more stones with veins as well as some with dendrites.