July 2020 – TumbleStone

The Iron-Stained Stones of Kai Iwi Beach

Google Maps view of Mowhanau Village (centre), showing Kai-Iwi Stream.

I moved to Whanganui from Cambridge just over six months ago. I now live quite close to the seaside village of Mowhanau situated on Kai Iwi Beach. I have walked on the beach a few times, especially near the Kai Iwi Stream mouth. I have not been particularly impressed with the few stones to be found amidst the scattering of stones and shells and other bits and pieces in the sand. They seemed to originate in a layer in the cliffs, and some were maybe being brought down by the stream.

Then I took a closer look at the small brown (iron-stained) stones lying here and there on the beach and in the stream. On this closer inspection, they looked like they might repay tumbling as there were hints of patterns within them and they appeared to be made up mainly of quartz, which polishes well. It took three weeks to tumble the first batch. The results surprised me. Here are four of the 60 polished stones.

Washed Kai-Iwi Beach stones, ready to be tumbled.

To take a closer look at two of these stones which have very different colours and patterns:

Here are three stones which are practically orange-coloured:

Three Kai-Iwi Beach polished stones of complex construction:

Some of the darker-coloured stones:

And, to finish off this part of the Post, three of the lighter-coloured stones:

What is the source of these stones? The following is a brief report on my initial investigations. Kai Iwi Beach is geologically part of the Whanganui Basin. This Basin has been described in “Landscape and Quaternary Environmental Change in New Zealand” (2016) as “a unique global archive”, unique because of the way it reveals “a shallow marine basinal sequence, exposed on land, which spans the entire Quaternary” (the last 2.6 million years). The cliffs and marine terraces along the coast from the mouth of the Whanganui River to the mouth of the Patea River expose a series of “sequences” of geological layering.

Source: https://link.springer.com/chapter/10.2991/978-94-6239-237-3_4

There are three parts to each sequence, described in a technical manner in a 1999 article in the New Zealand Journal of Geology and Geophysics as follows: The first part is “a basal suite of shore face and inner shelf sediments with intertidal and shallow subtidal molluscan faunas, and cross-bedded, pebbly shell gravels” – it is likely that the stones I collected and polished came from this kind of layer. The second part of each sequence is typically “a shellbed, which contains in situ offshore molluscs in a matrix of muddy fine sandstone or fine sandy siltstone”, with the third part being “siltstone, either bedded and barren of fossils, or bioturbated and with a sparsely scattered in situ fauna”. In other words, there are lots of layers here, many of which contain fossil shells and a scattering of stones.

The beaches along this coastline are often littered with rocks and stones that contain many fossil shellfish. A recent visit to the wild and secluded Ototoka Beach, not far from Kai Iwi Beach, resulted in many fossil shell finds.

The way down to Ototoka Beach from the carpark – Petra is on the bridge.

See here for a two minute YouTube video on Kai Iwi Beach – the first part is on the more popular part of the beach a few hundred metres to the southwest of the Kai Iwi Stream mouth. At 1 minute 15 seconds, the Kai Iwi Stream is shown, then the beach past the stream mouth.

This YouTube video features drone footage of Kai Iwi Beach. Most of the first part of the video is of the beach at Mowhanau Village but at 2 minutes 4 seconds it goes up the beach past Kai Iwi Stream, the area in which I found most of these stones, and it shows more detail of the stream itself from 2 minutes 25 seconds.

A YouTube video of drone footage of Ototoka Beach.

Fresh Batch of Polished Gemstone Beach Stones Collected by Helen

In June, when I was visiting Riverton and Gemstone Beach, my sister Helen accompanied me on some of my fossicking trips. She collected a few bucketfuls of stones and carefully selected some for me to take home and polish for her.

Helen on Gemstone Beach.

Today I completed polishing a 4lb barrel full. Included are a wide range of types and sizes of Gemstone Beach beauties. Here they are, in two trays:

A closer look at the first tray:

A closer look at the second tray:

These stones started out as relatively smooth beach stones. They tumbled in 320 silicon carbide grit for eight days and 19 hours, followed by a five hours soap tumble. A pre-polish in tin oxide was next, for just under eight days, followed by a five hour soap tumble. Finally, just under nine days was spent tumbling in pro-polish tin oxide, with a final burnishing tumble in borax for two days.

Photo-Book #2 “The 33 Stones of the Lockdown”

Photo-book number one.

Photo-book number two.

This is my second recent photo-book, using an online site. The first was on the trace fossil stones of Gemstone Beach. “The 33 Stones of the Lockdown” features the stones I posted on TumbleStone Blog over the 33 days of the Lockdown in New Zealand. The first Post of this Series, on Thursday 26 March, featured a small grey brecciated stone from Gemstone Beach.

I decided that a photo-book would be a great way to be able to look back, in the years ahead, on a significant and unusual time in the history of our communities, country and the globe. I no longer have all these 33 stones as I sent a few to those of my small number of Facebook friends who followed the Series on Facebook, so the photo-book is also a record of some special and unusual pebbles that I have collected and tumble-polished. Photos dominate the 30 page book, which is hardcover and 20 cm by 20 cm in size. At the beginning is a photo of all 33 stones followed by a brief introduction to the Covid-19 pandemic in New Zealand.

Photos of the 33 stones make up the bulk of the book. On some pages, just one stone is featured. On other pages, two stones are displayed. The online site provides a number of pre-determined formats and these two best fitted my aims.

It is difficult to control the brightness and colour of the finished product. What you see on your computer screen is not always an accurate representation of what turns up in the book. I order one copy of the book first and then make any adjustments required to ensure good images before ordering any further copies.

The final couple of pages have photos of the places where the stones were found.

Back cover.

All 33 stones, plus the other stones posted during Alert Levels Two and Three, can be found in the Summary Index of Stones of the Pandemic.

Photo-Book “The Trace Fossil Stones of Gemstone Beach”

Front cover.

Photos of trace fossil stones.

Back cover.

I recently sold some tumble-polished fossil worm cast stones to a Rock Shop. I thought I would provide the Shop with a photo-book about the stones so that customers would have a bit of background about them.

I have produced photo-books before about holidays and overseas trips, using DiamondPhoto, a New Zealand-based online site. I have also done some calendars through this site. Its products are quite good when working with photos but I sometimes struggle when text is involved – it can be tricky to place text correctly on a page. I chose to put together a 20 page book, 20 cms wide and 20 cms high, small enough to fit on a shop shelf but large enough for decent-sized photos.

The other tricky part of using an online site is getting the brightness of the photos right. How good a photo looks on a laptop screen depends on how tilted the screen is. I have learned to order an initial copy of a calendar or photo-book and check the photo quality and text placement before finalising a project.

The following are the front cover and first three pages of “The Trace Fossil Stones of Gemstone Beach”. The “Introduction” is important for such a book, giving the reader an immediate idea about the topic but also intriguing them to want to know more.

Front cover.

Introduction.

Contents of photo-book.

Photos of trace fossil stones.

There are four later pages on which text is provided in the book. The first (page 3) is a quote from Geoff Chapple’s book “Terrain: Travels Through a Deep Landscape” about the worm trace fossils at Tihaka, near Gemstone Beach. This provides verification for the nature and age of the trace fossils. Secondly, on page 5 is an introduction to “Trace Fossils” as one type of fossil, supported by photos providing the broader context of marine trace fossils in New Zealand. Thirdly, on page 6 is a brief reference to the diversity of the trace fossils in Gemstone Beach stones. Fourthly, page 13 contains a brief description of rotary tumble polishing.

This page faces the text about tumble polishing.

One of the key aims of the book is to show photos of the great diversity of trace fossil stones from Gemstone Beach. Another is to provide an appreciation of the beach on which they were found.

Some information about Gemstone Beach.

Gemstone Beach scenes.

Aspects of location.

More Gemstone Beach scenes.

Given that the book promotes a certain type of stone that I have tumble-polished, I decided to include other examples of my tumble-polished stones from different places: Gemstone Beach, Birdlings Flat and Riverton. The book finishes with some information on TumbleStone Blog – in case someone wants more information about trace fossil stones – and a list of the sources of information used.

Back cover.

I have done one other photo-book on stones and am thinking of a couple more. But they take time and patience, and I am intending to undertake another stone collection trip to the South Island soon.