Updated: Oct 1, 2020
Based on 'Rock glazes of NZ' Minna Bondy
Sample 20 Reddish Scoria
A maroon coloured fine-gra ined volcanic rock rough to the touch, showing numerous tiny cavities produced by the expulsion of gas from the original volcanic lava; widespread in the Auckland district and to a lesser extent the Lyttleton and Dunedin Areas. Composition will be variable but lying approximately around that of andesite.
Roadside cuttings are by far my favourite gleaning spot for materials as you feel like you doing someone a favour by cleaning up.
This spot on the summit road was crumbling and a recent slip had left some pretty big chunks on the edge of the road. This scoria doesn't look much like the kitch, mid-century garden variety, as it's much rawer and varied in colour. I couldn't resist adding an example from one of my favourite gardens in Taranaki.
I also gathered another sample that the local potters spoke of as a type of Loess. It's a much finer grain and clay-like consistency. I'm unsure what its composition actually is, and will do more research as Banks peninsular has pockets of red ash, and it could possibly be that.
The road between Lyttleton and Sumner has more examples of "red rock". The red rock retaining wall on the Lyttleton/Sumner road is impressive, and a huge quarry reveals the layers of coloured rock on a massive scale (see diggers). The quarry was closed when I passed but I will endeavour to obtain some rock to test from this site.