GEORGE BERNARD / SCIENCE PHOTO LIBRARY GEORGE BERNARD / SCIENCE PHOTO LIBRARY
Marble. Cut surface of marble, a type of metamor- phic rock derived from limestone. Pure marble con- sists only of the minerals calcite and dolomite, and is white. The colours here are caused by impurities of other minerals. Marble is formed when limestone is subjected to intense heat and pressure, which cause the calcite in the rock to recrystallize into coarse, interlocking grains. This rock has been subjected to a second form of metamorphism that has broken up the marble into angular fragments (breccia) cemented together by finer material. Marble, both raw and polished, is widely used in building. This sample is from Portugal. Magnification x0.25 at 35mm size.
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