Based on 'Rock glazes of NZ'
Minna Bondy
Sample 12. Semi Schistose Argilite or fine-grained Greywacke
This hard blue-grey rock a strongly indurated mudstone. It shows a tendency to split into irregular sub-parallel layers. Widespread in New Zealand and commonly interbedded with Graeywacke
Sample 23. Argillite (Waihi)
See Argilitite No. 12
When testing the argillite I choose to use crushed rock from a quarry close to Waihi as I could be assured that it was defiantly argillite. From a sample of mixed grade rock, the material was then sieved through a 50 mesh sieve.
The rock at Green Point (below) was also said to be Argillite but I couldn't clearly identify the sample so I choose to use the Quarry sample above.
When studying up on Bluff Gabbro I saw it was located at ocean beach. Ocean beach is a thin strip of land that connects Bluff with the mainland. I was convinced it was the easiest place to source Gabbro and on this bleak sleety morning. Greenpoint is signposted clearly as a ship graveyard, 'rotten row which was also kind of enticing.
There are large areas of what looks to be thick black basalt lava, then exposed Argillite further toward the point. Signage tells the story of the old shipping docks and some of New Zealand's oldest rocks laid as marine sediment 270 million years ago. Thirty million years later was the volcanic activity that laid the basalt.
The Argillite was used by early Maori for manufacturing stone tools. Opposite at Tiwai point large quantities of tools dating to the 13th century and remnants of a seal butchery were found. Sadly today the point is a huge obnoxious aluminium factory and along with another unsightly decaying factory at ocean beach this area awfully industrial. If you can see past the 20th-century decay the rock is some of the most incredible I have seen on this trip.
Excited and confused by all the varieties of rock I only grabbed a very small quantity of something that was neither Gabbro nor Norite. The samples are potentially Basalt, Dunite and Argilitte and also a semi schistous Argillite that Bondy refers too, though this location wasn't listed in her book.