This is a thin section (a microscope slice, 3 millimetres wide) of greywacke – an assortment of angular grains in a fine-grained clay. The clear grains are mainly quartz, while many of the cloudy grains are feldspar.
Te whakamahi i tēnei tūemi
Photograph by Nick Mortimer
Permission of GNS Science must be obtained before any use of this image.