I recently presented 12 of my polished stones to a work colleague in appreciation.
I took on the job of Assistant to an AB Technician in the dairy industry for three weeks, at the height of the insemination season. This was a completely new experience for me and I enjoyed it a lot, largely due to the support and patience of Tony, the Technician I was assisting. I chose to give him 12 stones because I spent a lot of time preparing the 12 inseminator implements that he regularly used. Below is a photo of inseminators being loaded (a straw of bull semen is loaded into the end of each inseminator, its plug snipped off with scissors, then a plastic sheath is threaded over it to hold in place).
These are the twelve stones:
I am taking the opportunity in this Series of Posts to dig into aspects of different types of stones and the places from which they were collected. This first Post will describe Stones #1 to #3, with the rest dealt with in Parts Two, Three and Four.
1) Stone #1 Dark Red Jasper
I found a rock in April 2016 near Waikaka in Eastern Southland. It was embedded in a farm track on “The Mains”, the farm on which I grew up. Red Jasper is a rock to be found as part of the Waikaka quartz gravels which contain the gold mined in the area between the 1880s and 1920s. There is an old gold dredging pond about 100 metres north of the track. I extracted this large Jasper rock and took it home with me to Karapiro on the plane. Later I broke off a few pieces to tumble-polish. Due to the brittle nature of the rock, I did not completely smooth the stones out before their final polish. (Click on the photos below to view them and see their accompanying captions.)
The farm track on “The Mains” – when it reaches the trees, it crosses the Waikaka River on a bridge. I found the Jasper rock about 30 metres from this point.
I broke a number of pieces from the Jasper rock in order to tumble polish them. I used a geological hammer (and I wore gloves and safety glasses while doing this), The pieces were sharp and a bit brittle.
The Jasper rock embedded in the track.
After being dug out and washed.
Not a good colour as this was taken inside, with poor lighting, but this gives an idea of the size of the Jasper rock.
A number of the Jasper fragments before being tumble polished.
After tumble polishing for about five weeks. Stone #1 is in the top row, far left.
Location of Waikaka at the bottom of the South Island (source: Google Maps):
More on Jasper as a gemstone.
Other TumbleStone posts referring to “The Mains”: Maps as a Resource: New Zealand’s “Maps Past”, Part One; Maps as a Resource: New Zealand’s “Maps Past”, Part Two; Jasper Stones and Petrified Wood, Shepherd’s Creek, Waikaka; and “You run from the river, when it long ran over you…”
2) Stone #2 Granite or Basalt Porphyry, containing Feldspar Crystals
I found this stone at Riverton, Southland, in September 2018. This type of stone, while not numerous on Riverton beaches, is not rare and one is likely to be found within 10 to 15 minutes of searching. Its most obvious and interesting characteristic is the lighter-coloured feldspar crystals packed into the darker surrounding matrix. This indicates the stone is of volcanic origin, and is probably either basalt or granite. “Porphyry” is a term for the texture of an igneous rock consisting of large-grained crystals, such as feldspar or quartz, lodged in a fine-grained silicate rich matrix. These crystals formed within magma underground – this material then reached the earth’s surface and cooled relatively quickly, “trapping” the crystals in fine-grained rock. The crystals can vary in size, as shown in these three photos from the Riverton Museum “Te Hikoi” (these photos were taken with the permission of Museum staff in December 2016):
Riverton Museum (photo taken with permission)
Riverton Museum (photo taken with permission)
Riverton Museum (Photo taken with permission)
The Riverton Museum often has a display of local stones types, usually set up for children. The well-known geologist Hamish Campbell has been instrumental in putting this together. In 2017, the Museum developed a five-page pamphlet as a guide for children and families to collect nine different types of stones from the area between Riverton and Orepuki.
Riverton Museum Guide Children’s Rockhound Club Adventure p.4
Riverton Museum Guide Children’s Rockhound Club Adventure p.2
Rock Type 1 “Volcanic Rocks” would include Granite and Basalt Porphyry. Reference.com provides the following explanation of the differences between Granite and Basalt: Granite is an intrusive rock that is formed when magma cools inside the crust. This slow cooling gives time for crystals to grow, making it more coarsely grained than an extrusive rock, formed at the earth’s surface. Basalt, on the other hand, is an extrusive rock, with a smooth texture from rapid cooling, usually by water. Granite has a high silicon content; it is mostly made out of quartz, mica and feldspar. Basalt contains more calcium oxide, manganese oxide and iron compounds than granite. I am unable to exactly identify Stone #2. Granite stones can easily be found in the Riverton area (see Stone #4) but Stone #2 seems to be less coarsely grained than Granite.
Riverton’s Back Beach, on Foveaux Strait, a source of many interesting stones for polishing
Further to the west than the previous photo. The Back Beach lies just beyond the far-off point.
Riverton has many small beaches full of stones
Location of Riverton (source: Google Maps):
3) Stone #3 Unknown Variegated Green Stone
This stone, found at Riverton in February 2018, is darker green towards the thicker end, with the other end being a lighter green. When slowly rotated in the light, small specks of mica can be seen at the darker end. It is probably a metamorphic stone having been subject to significant heat and pressure at some stage. So I looked up metamorphic rocks in “A Photographic Guide to Rocks & Minerals in New Zealand” (2011), written by Nick Mortimer, Hamish Campbell and Margaret Low. Page 20 (see below) has a basic classification which led me to consider whether at least part of this stone could be “Hornfels”. Page 119 (also see below) mentions that Hornfels contains “small micas” and that some occur in the Bluff area, which is along the coast not far south-south-east of Riverton.
“Photographic Guide to Rocks & Minerals of NZ” page 20
“Photographic Guide to Rocks & Minerals of NZ” page 119
Many of the stones on Riverton beaches are thought to have come down the Waiau River whose mouth is about 50 kms westwards.
Stones are often unique in their shape, size and patterns, and contain a range of elements, layers, intrusions and so on, which make them very difficult to identify with certainty. Chemical analysis is often needed. Stone #3 remains unidentified.
Stones #4 to #6 are described in Part Two.
