Dolerite is composed of an intrusive volcanic rock of plagioclase feldspar that is harder than granite.
Sediments are up to 500 meters thick, with the lowest layers consisting of dolerite boulders.
The peak is sandstone with dolerite intrusions and is a sharp summit ridge.
Dolerite is intrusive and is relative to basalt (extrusive).
The pebbles are mostly quartzite, but include dolerite and agate.
The dolerite is believed to have existed as much as 1/2 billion years before the meteorite impact.
The lighthouse was built by convict labour using locally-quarried dolerite over two years.
Although they appear to be of abiogenic origin, only that near the dolerite sills points to a probable mantle origin.
