LL Demos & Labs: Rock Profile: Limestone, Lab: Acid Test
Limestone is an extremely common, light gray rock from Utah. It is made up almost entirely of very small crystals of the mineral calcite. Calcite fizzes when you drop an acid (vinegar, for example) onto it. So a quick and easy test for limestone is the fizz test. The calcite that makes up a piece of limestone can come from several places. In warm, marine water, calcite can precipitate directly from solution. This generally makes a fine-grained limey mud. Limey mud makes up the bulk of some limestone layers; it’s most often a bland gray color, but it can have earthy (red, pink, orange, yellow, green) colors.