Image: Porphyritic trachyte
Porphyritic trachyte (12.5 cm x 9 cm). Upper Fine Flower Rd, Coaldale area, New South Wales.
- Stuart Humphreys
- © Australian Museum
Trachyte is a volcanic rock composed largely of alkali feldspar. Porphyry is a general term for igneous rocks that contain phenocrysts (larger crystals) in a finer-grained groundmass.