The rock, which is believed to be the largest in the UK, was mined from a remote quarry called Boogardie station, a small settlement in the outback of Western Australia. This region of Australia contains very ancient parts of earth’s crust; the material from the quarry has been dated at more than 2.6 billion years old.
Orbicular rocks are not very common. Of the thousands of areas
of igneous rocks across the earth, less than 200 orbicular rock
occurrences are known. These include sites in Finland, Chile, the
Channel Islands and France as well as the Australian
material.
The specimen is polished all over to reveal the beautiful orb
patterns on the rock (see below), which are formed when magma
intrudes into the earth’s crust then cools.
At 1.7m high and weighing in at a hefty 870kg, it is set to become one of the key monoliths on the origin of rocks in the Earthworks gallery, which will examine the structure of the earth and its complex and varied history.
If you’re interested in finding out more about the orbicular
granodiorite, keep an eye on our object of
the month feature, where it will be appearing soon.