There are several natural stones used frequently in and around the home in tile and slab form. Included in these materials is the calcareous stone limestone. Limestone is occasionally referred to as "limestone marble" by vendors, which can confuse homeowners shopping for a specific stone. In fact, limestone is different from marble in both appearance and creation, although similar in mineral makeup.
One way that limestone's appearance differs from other natural stones is in its pattern. While marble is marked by veins and granite by a crystalline structure, limestone is studded with fossils.
Limestone is created out of a shell bed or reef in or near the ocean. Thousands of fossils ranging from the size of a pin to the size of an apple can be found embedded in the stone. Some limestones such as Cafe Pinta are known for the extreme fossilization, while others have only a few. Dirty limestone, or limestone that has been subjected to other minerals and dirt or mud, may also show waves of darker color. These waves may have an appearance similar to sand or mud.
Limestone is made primarily of calcite. Stones made up entirely of calcite will appear white or nearly white in color. Any stone that is made up of at least 50 percent calcite is still classified as a limestone, which means the stone could have several other minerals, which give it a color.
Limestone ranges primarily in light colors such as cream, yellow, gold and light gray. There are some darker limestones as well, such as Lagos Azul, a dark gray and Nero Caracol, a black stone studded with white fossils. Some shades of pale blue and pink can also be found, but limestone is found primarily in neutral colors.
Limestone differs in hardness, depending on what makes it up. Some limestones contain large amounts of dolomite, while others contain largely calcite. This means that some stones can be ground down to a high polish, while others are too soft and can only be ground to a honed or flat finish. All limestones can typically be found in honed finish, and all limestones can also be either tumbled or flamed to bring out an antiqued texture. French limestones, such as Beaumaniere, contains large deposits of soil and clay and therefore has a naturally textured finish. This finish can be ground to a high hone, but is still visible to the eye in waves and an obvious grain.
Because limestone is made up mostly of materials such as dolomite and calcite, which are carbonate, or which react to waters and acids, limestone develops a patina over time. Some stones will dissolve slightly in water, which means that stone subject to frequent exposure to moisture, such as those in a shower, or even entryways, will wear down slightly over a period of years. Pitting, softening and aging of the stone is natural over time. The stone may also darken as it absorbs minerals in water and it may etch when it comes in contact with acids. These qualities help develop a patina over the stone, which softens its appearance as it ages.