Recently I was wanting to buy some books on Scottish Island knitting patterns on behalf of my wife. I inquired at my favourite local secondhand bookshop, Book Hunters on Ridgway Street in Whanganui. There I spoke to Cam who said they had none in stock but he would look out for them, and he wrote my contact details in his book. Not long afterwards, he rang to say he had found a bunch. They were just what I was after, and he gave me a good deal on them. I knew he lived at Kai Iwi Beach so I asked whether he would be interested in a gift of some tumble polished stones from there. He said yes, so I have picked out 50 to give to him.
Kai Iwi Beach is my local beach and from time to time I walk Jasper the dog there. There are not many stones on that beach – in fact, the area is much better known for fossils, especially of moa. The nearby village is called Mowhanau and it is thought the name could have originally derived from “moa-whanau”. I automatically look for stones when I am on any beach. As a result, over the past few years I have collected quite a few from Kai Iwi Beach that I have gone on to tumble polish. Most of them are quartz that have been stained yellow-orange by iron oxide – see “The Iron-Stained Stones of Kai Iwi Beach”. A few other stone types occur, and I recently found a trace fossil in argillite and an orbicular jasper, both rare. With even ordinary appearing stones, however, when they are viewed up close, there is quite a variety of interesting colours and patterns in them.
The 50 stones given to Cam are presented in this series of Posts in no particular order. The first ten are below.
Stone 1 could be mistaken for a jasper, given its red hues. However, it is more likely to be quartz with its colour due to the presence of iron oxide:
Quartz is one of the most common minerals on Earth and is hard and glassy. Its purest form is rock crystal which is colourless and transparent. However, more often quartz stones incorporate other minerals which give them colour and make them opaque. Iron oxides include a number of chemical compounds such as hematite and limonite. They can colour stones a number of hues, from yellow to orange to red to brown and even black.
Stone 2 could be a mudstone because of its very fine grained and smooth character. Mudstone is a sedimentary rock, often laid down on the ocean bed. But what is most interesting about Stone 2 is that it has fragmented in places due to tectonic stress. Great weight of rock can move slightly and deform or break-up what lies beneath. The fragments in Stone 2 are angular which means the stone could be viewed as a kind of breccia – see “T is for a Type of Tiny Tectonic Breccia?”
Stone 3 is more typical than Stone 1 for the kind of iron oxide-stained quartz from Kai Iwi Beach, being more orange-yellow in colour. It is more spherical in shape than most of the stones on the beach which tend to have two distinct flat sides:
Stone 4 is made up of lots of tiny bits of quartz and other minerals. It could be a kind of sandstone, formed from the compaction of these tiny bits, though most sandstones have finer grains:
Stone 5 is another iron oxide-stained quartz but the mineral is distributed within the stone quite differently from Stone 3, with the quartz itself sometimes showing white around the edges:
Stone 6 appears in some ways to be a more compact version of Stone 4, made up of lots of tiny bits of quartz with iron oxide providing a yellow-orange colour:
Stone 7 is again likely to be made up primarily of quartz but there is a black mineral in it providing a different character to the previous stones:
Some stones look different on different sides. Stone 8 is an example of this. Again, it is an iron oxide-stained quartz, similar in many ways to Stone 5, but the distribution and pattern of the colour-providing mineral varies a lot on the two different sides:
Stone 9 has some similarities to Stone 4 but has more small dark mineral bits in amongst the tiny quartz crystals. I suspect some of the dark bits are biotite mica, which also sparkle when they catch the light just right:
Stone 10, the final one in this Post, is again an iron oxide-stained quartz. Some areas of the stone have no colour-providing mineral in it and it seems as though you can see into the quartz to some extent:
Stones 11 to 20 are described in Part Two.
I’ve always been interested to know how you store/categorise your finds – by location, by mineral, by colour? By all three or by none of those categories? Your collection must require a lot of storage space.
Hi Anna. I store my beach stone finds by beach and month/year. Knowing where a stone comes from helps to identify it. Once a stone is tumble polished, I sometimes will mix stones of different dates but always keep the places separate. When I’ve got a lot of stones from one beach, I sometimes store them by rock type (e.g., Gemstone Beach rhyolite, hydrogrossular garnet, poppy jasper, trace fossils etc). John