Puerto Rico Territorial Rock
Limestone STATUS Unofficial DESCRIPTION Limestone is a hard, fine-grained to very coarse-grained sedimentary rock, composed primarily of calcium carbonate, and typically white to buff in color. In general, limestone is more soluble than sandstone and thus more subject to weathering, which is very much in evidence in Puerto Rico. The local limestone is mainly karst, heavily eroded by tropical rain, river action, and subterranean water and therefore often porous and friable. The karst is also home to several freshwater aquifers, the largest of which extends over 1,000 square miles (1,800 km2). A TERRITORIAL SYMBOL While Puerto Rico has never designated an official territorial stone, limestone, which covers about a fourth of the main island, deserves consideration because it is associated with several distinctive geologic and biological features of the island. The northwestern part of the island is a geologic province known as the Northern Karst, made of eroded Miocene limestone generally around 20 to 30 million years old. The Cavernas del Rio Camuy, one of the world’s largest cave complexes, are carved by the world’s third-longest underground river. Mogotes, or "haystack hills," spreading across large areas, and sumideros, limestone sinkholes, are characteristic of Puerto Rico. Because karst environments harbor a great diversity of life, the territory is famously rich in flora and fauna. Thirteen hundred species have been identified in Puerto Rico’s karst ecosystems. FORMATION Limestone is a sedimentary rock that forms by accretion (accumulation) of coarse to very fine particles of shells and skeletons of mollusks or other larger invertebrates, corals, or single-celled organisms. Some very fine-grained limestone forms from chemically dissolved calcium carbonate, also generally of organic origin. The particles that make up the rock typically accrete in layers underwater, particularly in marine environments but also sometimes in freshwater. As layers are buried under layers, pressure accumulates, compacting the particles. However, the temperatures and pressures to which limestone is subjected are much lower than those for igneous and metamorphic rocks. Puerto Rico’s limestone formed undersea and was uplifted by the volcanic activity associated with the Carribean/Atlantic subduction zone. GEOGRAPHIC DISTRIBUTION Sedimentary rocks cover about 80 percent of the earth’s land and most of the ocean floor, yet they form a thin skin, accounting for only eight percent of the volume of the earth’s crust. Limestone specifically makes up about a quarter of this material. Because it lies at the surface, it is readily available all over the world. In 2005, U.S. quarries sold 581,000 metric tons of dimension (cut) limestone in the domestic market, of which 327,000 was dressed (precisely cut) and the rest was rough. USES Dimension limestone (limestone cut to shape) is used in architecture because of its beauty, versatility, and prevalence. It lends itself well to ornamental carving. However, the karst of Puerto Rico, being highly eroded, is not suited to these purposes. Limestone aggregate is used for industrial purposes such as roadbeds. Finely crushed limestone is used in papermaking to increase the opacity of paper; lime from limestone is used to make cement. Because of the high pH of calcium carbonate, crushed limestone is used in agriculture to counter acidity of the soil. PRODUCTION Puerto Rican quarries produced 8.7 million tons of crushed limestone and 1.6 million tons of Portland cement in 2006. FAMOUS EXAMPLES Limestone has been used for important buildings since ancient times. The Great Pyramid of Giza is made of limestone quarried near the construction site. The Western Wall of Jerusalem is one of the city’s many ancient structures made of local limestone. The famous medieval cathedral at Chartres, France, is made of limestone, as are the British Houses of Parliament and New York’s Empire State Building. Most well-known examples of karst are natural formations. The famous Three Gorges of the Yangtze River (Qutang, Wu, and Xiling Gorges) are spectacular examples.	Limestone Wall Limestone Formation Great Pyramid of Giza Is Made of Limestone Three Gorges of the Yangtze River Limestone Cavern LIMESTONE FACTS Name: Limestone Chemical Formula: CaCO3 Color: White or lightly colored, usually with dark streaks
	Author: World Trade Press