Month: August 2024

Selection of Tumbled Ward Beach Stones: Part 5 – Hard Stones

Ward Beach.

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:

Ward Beach stone.

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

Ward Beach stone.

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

Ward Beach stone.

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:

Ward Beach hematite jasper.
Ward Beach jasper.

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

Ward Beach stone.
Ward Beach volcanic stone.
Ward Beach volcanic stone.

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:

Ward Beach volcanic stone.
Ward Beach volcanic stone.
Ward Beach volcanic stone.

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

 

Selection of Tumbled Ward Beach Stones: Part 4 – Stones Containing Both Soft and Hard Material

Ward Beach stone.
Ward Beach, viewed from the south.

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. Part 5, the last in the Series, looks at hard stones.

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.

Ward Beach stone.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.

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:

Ward Beach stone.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.

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

Selection of Tumbled Ward Beach Stones: Part 3 – Stones With Veins; Stones With Dendrites

Ward Beach limestone(?) with quartz vein.
Ward Beach stone with dendrites.
Ward Beach stone.
Stones on Ward Beach.

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. All five Parts in this Series are set out in the Index here.  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:

Ward Beach stone.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.

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

Ward Beach stone.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.

“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:

Ward Beach stone with dendrites.
Ward Beach stone with dendrites.
Ward Beach stone with dendrites.
Ward Beach stone with dendrites.

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

Selection of Tumbled Ward Beach Stones: Part 2 – Other Limestone Pebbles

Ward Beach “ringed” stone.
Ward Beach veined stone.
Ward Beach stone with dendrites.
Ward Beach stone.
Ward Beach, in front of the carpark.

This five-part 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. The Series Index is here.

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:

Ward Beach limestone.
Ward Beach limestone.
Ward Beach limestone.
Ward Beach limestone.

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

Small Ward Beach pastel shade limestone pebbles.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.
Ward Beach stone.

 

Some limestone pebbles have thin veins running through them:

Ward Beach stone.
Ward Beach stone.

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

Ward Beach stone.
Ward Beach stone.
Ward Beach stone.

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

Ward Beach limestone.
Ward Beach limestone.
Ward Beach limestone.
Ward Beach stone.

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.

Selection of Tumbled Ward Beach Stones: Part 1 – Trace Fossils in Limestone

Ward Beach trace fossil stone.
Ward Beach “ringed” stone.
Ward Beach limestone(?) with quartz vein.
Ward Beach stone.
Ward Beach, in front of the carpark.

Two or three times a year, I drive from home in Whanganui to the South Island to collect beach stones. After the Cook Strait ferry crossing, and then again on my way north, I usually stay overnight at the Flaxbourne Motels in Ward, Marlborough. Occasionally I am able to visit nearby Ward Beach for an hour or two as well. The Motel is operated by Ronnie and Ian, who have shown interest in the Ward Beach stones I have collected and have been supportive of my blog. Last time I saw them, I mentioned I would bring them a few polished Ward Beach stones on my next trip. This Series of Posts describes some of the stones I will be dropping off, grouping them into six broad types, partly with the process of tumble polishing in mind. This first Post described limestone pebbles with trace fossils in them. Part Two features a range of other kinds of limestone. Part Three deals with two groupings: veined stones, and stones with dendrites. In Part Four I look at stones containing a mix of both soft and hard material. Part Five is about hard stones which are, of course, the easiest to tumble polish.

Limestone pebbles are reasonably common on Ward Beach, and indeed along the Kaikoura coast, and many of them contain trace fossils. A trace fossil is not the fossilised remains of a dead organism. It is a track, burrow or other kind of mark that relates to an animal’s (or plant’s) behaviour. A trace fossil is the record of an animal’s moving, exploring, hiding, breathing, hunting, feeding, excreting, playing, fighting, dying, or resting. An introduction to a kind of trace fossil that can be found at Ward Beach is in the Post “W” is for “Ward Beach Zoophycos”. As noted there, A Photographic Guide to Fossils of New Zealand has an entry (p.64) on these trace fossils: “This form has nested, U-shaped curving linear traces in the plane of strata; in three dimensions, it appears as a large auger spiralling through the strata…Ward Beach is famous for its smooth trace fossil-bearing pebbles.” The traces are due to the burrowing activity of some organism and were likely made between 35 and 84 million years ago.

Ward Beach trace fossil in limestone.

Ward Beach has quite a few trace fossil stones scattered across it. Being limestone, they are often dull due to the weathering of their surface. But if you look at them wet, the trace fossils are clear – that is why I often walk on the beach along the edge of the waves. I collect beach stones and them tumble polish them to make them smooth and shiny. I pick up stones that have interesting colours, patterns and lines, and I often don’t know what kind of stone they are. I discovered a few years ago that limestone is too soft for the normal tumbling process (four stages using different grit and polish, taking up to six weeks or so), 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 (400 size) grit, followed by a short soap tumble, would remove the cloudy surface and leave a nice smooth waxy-feeling stone. The waxy feel is unusual and distinctive. Tumbling doesn’t give such a stone a high polish, but its surface is permanently clear, showing the trace fossil well.

Here are a few of the Ward Beach trace fossil stones I am leaving with Ronnie and Ian. Some of them, like these five, have one, two or even three “standard” traces through them (most of these stones are between two and four centimetres long):

Ward Beach trace fossil stone.
Ward Beach trace fossil stone.
Ward Beach trace fossil stone.
Ward Beach trace fossil stone.
Ward Beach trace fossil stone.

Other stones have unusual trace shapes or sizes – six examples:

Ward Beach trace fossil stone.
Ward Beach trace fossil stone.
Ward Beach trace fossil stone.
Ward Beach trace fossil stone.
Ward Beach trace fossil stone.
Ward Beach trace fossil stone.

Other limestone pebbles have plainer dark markings, lacking “nested, U-shaped curving linear traces” – these may be other kinds of trace fossils or simply different, and darker, sediment layers:

Ward Beach limestone pebble.
Ward Beach limestone pebble.
Ward Beach limestone pebble.

The next Post in this Series features other limestone pebbles I have found on Ward Beach.