limestone is a fairly common type of sedimentary rock that forms near waterways and can be found, although rarely, where ancient bodies of water used to be. This is because limestone is typically made of calcium that comes from marine creatures. There are sometimes other impurities that can be found in limestone, which create different varieties and colors of the rock. Overall, it makes up about 10 percent of all the sedimentary rock on Earth.
Limestone is composed mainly of a mineral called calcite, which is composed of calcium, carbon and oxygen. The calcium that makes up the particular calcite in limestone typically comes from marine life. This includes corals, which have a heavy calcium composition, and the shells of mollusks and other animals that are discarded onto the ocean floor. Not all limestone is pure as it is formed, though. Many times, impurities such as sand, various crystals, clay or other things are also mixed to create limestone with different colors and textures.
Pure limestone is very easy to spot. Because it is composed nearly entirely of calcite, the rock has a white or near-white color. This color can vary with limestone that has hardened after other impurities have mixed with the calcite. Clay that is present, for example, may give the limestone a brown or red-brown coloring. The limestone can also be smeared with rust, which occurs from various crystals and metals that may be present in the rock. If it is, you will see a copper smear across the surface of the rock. The rock itself is usually smooth on at least one side because it is created near waterways that often erode its surface.
There are a couple of different types of limestone, created by some of the more common impurities found in it. The most common is travertine, which is found among streams. Much like a casserole of minerals and composites, this form of limestone is banded so that each layer is clearly visible. Coquina is another type of limestone that has been created entirely from shells and bits of coral, making it unique to coastal areas.
Limestone is a common and significant material found in architecture. In the past, many world marvels, such as the pyramids, used ancient limestone that was created when there was water present instead of desert. Today, architects use limestone in many buildings, though it is most commonly used in North America and Europe. In particular, it is so prevalent in the city of Kingston, in Ontario, Canada, that the place is nicknamed the “Limestone City.”
If you are using limestone in architecture, it is important to know that the stone does not hold up to everything. In particular, it has a weakness to acid. In areas of the world where acid rain has high chances of occurrence, limestone structures will break down If exposed to it. Even the acidic content in water can break down limestone over time. The same goes for anything made of limestone. Many older sculptures show sign of damage from water that has occurred over time.