Granite is an igneous rock formed from liquid magma, cooled slowly to form a substance approaching the hardness and durability of diamond. Its hardness and density comes from the fact that it has been solidified within the earth under extreme pressure. It consists of feldspar, quartz, mica and other minerals that all contribute to the unique coloration and texture of each granite deposit. Granite is considered ideal choice for kitchen countertops because it can withstand high heat (up to 1200 degrees Fahrenheit). Granite countertops are also scratch resistant and can hold up with heavy use.
Marble is a metamorphic rock formed from the re-crystallization of limestone under intense pressure and high temperatures within the earth. During this process, other minerals are introduced into the structure, which produce beautiful colors and veining which characterize marble. Marble colors vary from white to black, being sometimes yellow, red and green, and frequently beautifully veined or clouded. Marble is scratch and stain-prone, as it is not as hard as granite surface. It is not preferred in the kitchen, but works well in bathrooms, on hearths and in some furniture applications.
Limestone is a sedimentary rock composed largely of the mineral calcite, most commonly coming from marine organisms. Limestone often contain various amounts of silica, as well as silt, clay and sand. Domestic limestones are grey to buff in color, while imported limestones contain colors from beige to dark brown, yellow, red and black.
Travertine is a sedimentary rock, mostly made of calcite that was generated by the deposit of such minerals from hot water springs and streams pouring from them. It is a very porous material, and holes are generated either by gasses trapped by the sediments or by water plants that were trapped inside the formation and then decomposed. It is highly susceptible to heat, scratching, staining, and acidity, and is not recommended for kitchen projects.
Onyx is the result of water dissolving existing limestone and re-depositing it as a new kind of stone. In limestone caves, onyx is formed by drip water, like stalagmites and stalactites. Onyx is best for furniture pieces, bathrooms and fireplace surrounds.