MICHAEL SZOENYI / SCIENCE PHOTO LIBRARY MICHAEL SZOENYI / SCIENCE PHOTO LIBRARY
Ancient Roman columns. This shows two types of rock used to make architectural columns. At right is a very coarse-grained granite, while at left is a far finer-grained one. The colours in the column at right indicate different minerals in the matrix: quartz is white, plagioclase feldspar is grey and mica is black.
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