Mica has a shiny flaky look, and is one of the main components of granite and gneiss, which are the common rock types you’ll find around Hoedspruit. Next time you find a piece of granite or gneiss, have a careful look for shiny mica flakes in the mix of minerals.
There are several varieties of mica, with the two commonest in this area being Muscovite and Biotite. Muscovite is clearer, and can form very large sheets, whereas Biotite is smaller darker flakes, and usually found in Granites and Gneisses.
Big sheets of mica are used for electrical insulation. If you look into certain toasters, the flat plate that the elements wrap around is made of mica.
In the past, very large sheets were used to make windows.
Another popular use is in cosmetics – the rock is ground into fine flakes that add shine and sparkle to makeup.
Mica flakes are also added to paint to make it tougher and more weatherproof. The name of a popular building and hardware chain in South Africa probably comes from this property.
Mica is also found in sedimentary rocks, often as small shiny flakes in sandstone and shale.
On the way from Hoedspruit to Mica, (named after the large deposits of high quality Muscovite mined there), just before 3 Bridges, there is an outcrop of schist on the left-hand side of the road. It contains prominent flakes of mica, formed by continent-building processes on the very early earth.
There are many interesting facts about mica. The word mica is said to have derived from the Latin word mica, which means ‘a crumb’. It is said that this name was probably influenced by the word micare, which means ‘to glitter’.
Biotite was named after Jean-Baptiste Biot, a 19th-century French physicist who studied the optical properties of micas; and muscovite was originally called “Muscovy glass” because it originated from the Muscovy province of Russia.
Micas are found in all three major rock types — igneous, sedimentary, and metamorphic.
The use of mica by humans dates back to prehistoric times. The civilisations in Rome, Greece, Egypt and China all had knowledge of mica and its uses. Even the Aztecs utilised mica. The earliest use of mica by humans is said to be found in cave paintings that date back to the Upper Palaeolithic period from 40 000 BC to 10 000 BC.
The largest crystal of mica was found in a mine in Canada and it was some 10m x 4m x 4m and weighed about 330 tons.
The value of mica is attributable to its unique physical properties. Amongst many properties, sheets of mica are inert, elastic, platy, very light, insulating, flexible, hydrophilic, they differ in opacity from opaque to transparent, and they are reflective, refractive and resilient.
As you can see, mica is an impressive mineral.
John has a continuous curiosity and an abiding passion for sharing the stories of South Africa’s remarkable biodiversity, rocks and landscapes. Based in KZN, he offers geological learning adventures throughout South Africa. Check out www.johnroff.co.za
