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

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.