limestone

The physical weathering and erosion of a limestone landscape. The freezing and thawing of rain and its mild acidic properties cause cracks and joints to enlarge, forming limestone pavements, potholes, caves, and caverns.

Biological weathering is an important form of rock breakdown on rocky coasts. Many organisms, such as barnacles and limpets, secrete organic acids that help to dissolve the rock. This is especially important in rock pools, where there is only a small amount of water. This means that the water can become quite acidic and break down the rock. It most commonly affects limestone and chalk, although it is also important for its effects on granite.

A limestone sink hole in Oman. Sink holes can be many metres deep, and often lead to underground caves. They are usually formed when water dissolves the edges of a join or crack, gradually enlarging it.

Rocky outcrops on the Aran Islands, in Galway Bay. Farming, along with fishing, is a key economic force on the islands, but scarcity of fertile soil is an ongoing problem. One traditional method of creating topsoil was to mix sand and seaweed gathered from the shores, and spread them on the fields.

Sedimentary rock composed chiefly of calcium carbonate (CaCO₃), either derived from the shells of marine organisms or precipitated from solution, mostly in the ocean. Various types of limestone are used as building stone.

Karst is a type of limestone landscape. Caves commonly occur in limestone. Marble is metamorphosed limestone. Certain so-called marbles are not in fact marbles but fine-grained fossiliferous limestones that have been polished.

Limestone

Town in northeastern Maine, on the New Brunswick border, 16 km/10 mi northeast of Caribou; population (1990) 9,900. It is situated in a potato-growing area. The Loring Air Force Base stimulated an economic boom after it was established here in 1947; it closed in 1994.