Image: Amygdaloidal basalt
Amygdaloidal basalt (9 cm x 6 cm). Tylden Quarry, near Woodend, Victoria.
- Stuart Humphreys
- © Australian Museum
Amygdaloidal describes a volcanic rock containing mineral-filled cavities (or vesicles). Basalt is the most common volcanic rock on Earth. Composed of essential calcic plagioclase and pyroxene, sometimes with olivine, feldspathoids or interstitial quartz. It is classified as a basic rock.