Limestone

Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO₃), typically white in colour and fine-grained. Sedimentary rock forms from material that accumulated and was compacted over long periods.

In Somali, the word 'tamaashiir' is often used for the common writing implement used on classroom slates. This tool is nowadays seldom made from natural stone; most are produced from gypsum or other bound materials.

Formation and characteristics

Limestone forms from the shells and skeletons of tiny sea organisms. When these creatures die, their remains sink to the sea floor and accumulate in layers. Over time and pressure, these layers become hard, fine-grained rock. Limestone is porous and absorbs water, which affects how groundwater moves through areas where it is abundant.

Uses

Beyond use as a writing slate, limestone and similar limestone rock are employed in cement manufacture, in agricultural lime to adjust soil acidity, in pigments, and as fillers in paint and paper. In some games, such as billiards, a chalk-like substance derived from limestone is applied to cues to increase grip.

Chemical reaction

Calcium carbonate reacts readily with acid, releasing carbon dioxide gas. This reaction alone is commonly used to identify limestone. When heated to high temperatures, it converts to calcium oxide, which is used in construction and cement.