A fine-grained form of greywacke in which the particles are smaller than sand.
Greywacke is a muddy sandstone sedimentary rock that is the foundation of New Zealand (and the continent of Zealandia). It formed from material deposited in the sea off the eastern shores of 'Australia' when it was part of Gondwandaland.
Sedimentary. Formed by moderate pressure and heat.
Size: Hand specimen.
Demonstrates erosion to a smooth oval shape due to movement down rivers and the coastline.
Images are examples of specimens only. Sizes and shapes may vary.