Aryeh E. Shimron

A “thin section” of a limestone fragment as seen under an optical microscope. At the top is a white crust on the limestone that was initially thought to be plaster. But this image proved otherwise: A tiny veinlet (a stylolite) of clay-ey material passes from the limestone into the white crust, changing color as it does so, from yellow at lower left to rust red as it proceeds toward the outside, to black as it enters the white crust. The veinlet changes color as it passes from the unaltered limestone to the burned limestone at increasingly higher temperatures due to changes in veinlet mineralogy. That the veinlet passes into the white crust demonstrates that the white crust was part of the ancient geological element of the limestone and not a plaster covering added in historic times. The white crust was formed at a temperature above 800 degrees centigrade.