Vesicular basalt arising from extruded magma in which gasses have expanded to produce cavities in the rock.
This basalt occurs as microphyric olivine basalt, vesicular olivine basalt and scoriaceous basalt. This specimen is of vesicular olivine basalt arising from one of several volcanic cones west of Biggenden , Qld, erupting during the Pleistocene. In some locations, such as in the Coulston Lakes NP, agglomerate can be seen containing vesicular basalt fragments.
Images are examples of specimens only.
Size and shape may vary.
Specimens are usually no smaller than 75mm in one dimension.