Hobbies And Interests
Pisolitic Limestone
Pisolitic limestone is white or yellowish brown. Its texture is made interesting by pisolites, spherical bodies over 2 mm in diameter made out of calcium carbonate. Pisolitic limestone comes from the precipitation of calcite and other minerals from warm, turbulent water. It's found in the Bahamas, the Great Barrier Reef of Australia and in some European hot springs. Pisolitic limestone is only of interest to collectors, because it has no industrial value.
Fossiliferous and Compact Limestone
Fossiliferous limestone can come in many colors ranging from white to black, depending on the minerals contained in it. The rock often has cavities because the fossils in it have dissolved. In many specimens the fossils can be clearly seen as shells or skeletons or imprints. Fossilized limestone found in the Nile Valley was used to build the pyramids, and this sort of limestone in general is very good for construction work. When crushed, it's good for ballast for roads and railroads. Compact limestone is hard, comes in many colors and has a very fine grain. It is often cut into slabs, polished and used like marble.
Chalk and Coquina
Chalk is a soft, fine form of limestone made of calcite, created in the ocean from the shells, or tests, of single-celled organisms. The White Cliffs of Dover are made of chalk. Limestone chalk is what's used on blackboards. Coquina, on the other hand, is a coarse material made of broken shells, coral and other organic detritus loosely held together by calcite. Still, it's a very durable building and paving material.
Travertine
Travertine is a light-colored limestone deposited from solution in ground and surface water. If it's very porous, it's known as tufa stone or calcareous sinter. When travertine is compact and can be polished, it's known as onyx marble. Travertine forms stalactites, calcite deposits that hang down, and stalagmites, calcite deposits which point up, in limestone caves. It's found most famously in Tivoli, Italy where it was used as architecture in the famous gardens, and in Sichuan, China.