Part One of this Series, about 12 stones, can be found here. The four Posts in the Series each describe the characteristics and origins of three different stones. This Post describes Stones #10 (from Riverton), #11 (from Birdlings Flat) and #12 (from Hokitika).
10) Stone #10 Whitish Quartzite stone with Clear Silica Inclusions, found at Riverton.
I have explained the origins and characteristics of Quartzite in relation to Stone #7 and have provided photos of Quartzites from Birdlings Flat in relation to Stone #8, both in Post Three. Quartzite stones can be found in a number of locations in the South Island. They can have a wide range of colours. One of their frequent characteristics is the clear inclusions of silica running through the stone. Quartzites polish outstandingly, due to their hardness and colours.
For the location of Riverton, see the end of the section on Stone #2 in Part One.
11) Stone #11 Banded Agate, found at Birdlings Flat.
Malcolm Luxton is a collector of Agates. He lives in Ashburton, close to New Zealand’s greatest agate-bearing locality of mid-Canterbury. In his excellent book, “Agates of New Zealand” (2015), he provides hundreds of photos of cross-sections of Agate rocks and stones he has collected from throughout New Zealand.
Luxton offers this explanation for the origin of Agate:
An agate…is a stone that formed as a secondary filling in the various shaped cavities generated or forged within…lava flows. Initially these cavities were created by trapped gases or liquids or by geological processes that produced cracks or ruptures. The secondary filling permeated the lava as a silica-rich solution, and…solidified inside these cavities, thus replicating the shape of its magmatic womb. If additional materials were present, either in the silica-rich solution or growing in the cavity prior to its introduction or introduced as by-products from the surrounding lava, those minerals may have been responsible for structures, assemblages and colours (page 16).
Luxton notes that much Agate material is discharged by Canterbury rivers into the sea and some of it is cast back onto more than 100 kms of Canterbury beaches. The movement of Agates by northerly coastal currents “accounts for the notoriety of Birdlings Flat as an agate-collecting destination” (Luxton, 2015, page 250). He then refers to Vince Burke’s collection in the Birdlings Flat Gemstone and Fossil Museum.
Upon my visits to Birdlings Flat, I have collected a few Agates, mainly quite small ones, though my wife Petra is much better at spotting them than I am! Some of the Agates I have found are just plain cloudy silica, some are banded to some extent, some have a little colouring.
For the location of Birdlings Flat, see the end of the section on Stone #8 in Part Three.
12) Stone #12 White Quartz, found at Hokitika.
Quartz is originally a clear crystal. When subject to heat and pressure, and when water is introduced into it, it becomes white in colour, the colour of the common white “Quartz” stone found plentifully on beaches in New Zealand. However, strictly speaking, this is “Quartzite” rather than “Quartz”, though the latter term is the most common for this white stone. For that reason, and in order to distinguish it from Stones #8 and #10, I will call it “Quartz”.
When walking beaches, it is the bright white Quartz stones that seem to claim the first attention of the collector’s eye. I have collected and polished many white Quartz stones from the beaches of Southland, Canterbury and the West Coast. And it is the West Coast where perhaps the best examples can be found, perhaps due to the closeness to the Quartz source, in the Southern Alps.
Stone #12 was found on the beach just on the south side of the Hokitika River, less than five kms from Hokitika town. I visited there on a dull, cold, rainy day in June 2016. The beach was quite sandy but receding waves revealed drifts of stones. There were signs of coastal erosion, with flax plants being undermined and uprooted, and the end of the gravel road had been washed away.
Location of Hokitika (click on image below, left), and location of beach near Hokitika where Stone #12 was collected (below, right) (source: Google Maps):
This brings us to the end of this series of Posts.