Picture of the Week
The kind of matter and energy we can see and touch – whether it is in the form of atoms and molecules, or heat and light, only forms a tiny proportion of the content of the Universe, only about 5%. Over a quarter is dark matter, which is totally invisible but whose gravitational attraction can be detected; while over two thirds is dark energy, a force that pushes the Universe to expand ever faster.
18 November 2013
This artifact from UCL's collections looks like it could be in outer space. But the interplay of light and chemistry that produces these shimmering colours has its feet firmly on -- or even in -- the ground. It is a close up of a polished sample of Labradorite, a type of mineral commonly found in the Earth's crust.
Labradorite is a type of feldspar. Feldspars are a family of common crystalline rocks, composed largely of aluminium, silicon and oxygen, with smaller quantities of sodium, potassium or calcium. Feldspars crystallise in hot magma as it cools down.
The green, shimmering quality of Labradorite (named after the region in Canada where they are commonly found) is caused by the structure of the mineral, which is made up of numerous thin sheets of transparent crystal.
Photo credit: UCL Geology Collections
High resolution image
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