Thin sections are slices of rock, mounted on glass, that are ground thin enough to transmit light. This allows microscopic examination of crystals, grains, fossils, and rock fabrics. Thin sections are of special value to three groups of paleontologists: 1) taxonomists studying groups whose classification rests on internal features or skeletal fabrics (such as foraminifera, stromatoporoids, some coelenterates & bryozoa, etc.), 2) paleoecologists interested in reconstructing biofacies from sand-size skeletal fragments, and 3) those interested in diagenesis of fossils and initial mineralogy. Almost anything can be made into a thin section, although metals and certain opaque minerals will not transmit light.