Question

Imagine you are walking in the woods and you come across a gray rock composed of a number of different fossilized organisms such as crinoids, trilobites, and brachiopods, you pour some hydrochloric acid on the rock and notice that it reacts to the acid. Based on this information, what is the name of this rock and what does it tell you about the environment in which it formed? State your answer in complete sentences.

Answer 1

The rock that was found is limestone. Limestone is a sedimentary rock that is created by marine organisms. When the organisms die, their bodies settle to the bottom of the ocean or sea, decompose, and all that's left is their skeletons. Those skeletons then compact over time until they're formed into limestone. It's mostly composed of calcium carbonate which does react with acids to produce carbon dioxide and water. The presence of limestone indicates that the area used to be under water. The presence of the fossils in the gray rock indicates that it is limestone instead of marble which is a metamorphic rock made from limestone that's been subjected to great heat and pressure. If the rock were marble, then there would be no fossils still in it.