Updated: Sep 29, 2020
Based on 'Rock glazes of NZ'
Sample 2. Gabbro
A rather dark crystalline rock with grain-size averaging about 2mm. Visible minerals are pyroxene and feldspar.
Not common in New Zealand two localities are North cape and Otama, Southland (the rock at this latter locality is rather altered) Essentially soda-lime feldspar and pyroxene.
Sample 5. Norite
Norite is identical with Gabbro (see no.2)
Norite outcrops extensively at Bluff, Southland. Essentially lime-soda feldspar hypersthene and iron ore.
Not everyone can say they have been to Bluff three times this week, but I can. The weather was bleak and could probably account for why I rushed and got the wrong rock (see tomorrows blog). The www.geotrips.org.nz site again proving to be the best site with clear information on how to identify samples.
From my understanding, this rock has been altered by volcanic lava flows which have heated and cracked the gabbro, allowing the basalt to form in the gaps. The black lines you can see in the images is the basalt in the gabbro. Please, if you are a geologist and can explain this better please do!
Gabbro Norite or Gabbronorite as I have seen it referred to is easily identified by its speckled appearance. It's very similar in appearance to the volcanic rock around Taranaki that makes a beautiful metallic teesha glaze, so I'm excited I finally got this one right!