ORBICULAR GRANITE - Australia
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ORBICULAR GRANITE
Polished section through a single 'orbicule'
2.7 billion years old
Boogardie Station, near Mount Magnet, Western Australia
Orbicular granite is one of the rarest and most extraordinary rocks in the world. Like normal granite it is formed from the crystallisation of hot molten magma deep underground and classed as an igneous rock. However, unlike normal granite the crystals have not grown in all directions but have grown in alternating layers of dark and light minerals to make the shape of a ball.
These ‘orbicules’ slowly sunk to the bottom of the magma chamber and accumulated to form this remarkable rock. As they settled they were still in a plastic state as they are often deformed and squashed together. The minerals are dark-coloured hornblende and biotite mica with pale feldspar.
Orbicular granite is quarried mostly for high-value ornamental works and sculptures. This example is a polished section through a single orbicule.
Click on a picture for a larger image
Size: 12 x 7 x 2 centimetres
Weight: 370 grams
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