- Limestone (calcium carbonate CaCO3) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of CaCO3. Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life.
- Rock of Gibraltar (Wikipedia)
The Rock of Gibraltar (from the Arabic name Jabal Ṭāriq جبل طارق, meaning “Mountain of Tariq”) is a monolithic limestone mountain 426 m (1,398 ft) high dominating the western entrance to the Mediterranean Sea. It is situated near the end of a narrow 9 kilometres (5.6 mi) long promontory stretching due south into the Mediterranean Sea and is located within the British territory of Gibraltar, and is 27 km north-east of Tarifa, Spain, the southwestern tip of Europe on the Iberian Peninsula. The rock serves as an impregnable fortress and contains a labyrinthine network of man-made tunnels known as the Tunnels of Gibraltar. Most of the Rock’s upper area comprises a nature reserve which is home to about 300 Barbary macaques. It is a major tourist attraction.