prize9-2, Exercise 2: Granite and gneiss

Model answer (check the details):

Minerals: both are made largely of quartz, feldspar and mica or similar minerals, so their make-up is close.

Texture: granite is igneous, with randomly oriented interlocking crystals that grew from slowly cooling melt. Gneiss is metamorphic, with the minerals sorted into light and dark bands by heat and pressure.

Why they look alike: similar colours and coarse grain size. The banding in gneiss is the key difference, though in some samples it is faint, so look at a larger piece.

Care: a rock name depends on both composition and texture, so describe both.