The density of limestone depends on its porosity, which varies from 0.1% for the densest limestone to 40% for chalk. Limestone that is unusually rich in organic matter can be almost black in color, while traces of iron or manganese can give limestone an off-white to yellow to red color. Limestone is commonly white to gray in color. Limestone often contains variable amounts of silica in the form of chert or siliceous skeletal fragments (such as sponge spicules, diatoms, or radiolarians). Organic matter typically makes up around 0.2% of a limestone and rarely exceeds 1%. Most limestone is otherwise chemically fairly pure, with clastic sediments (mainly fine-grained quartz and clay minerals) making up less than 5% to 10% of the composition. Aragonite does not usually contain significant magnesium. High-magnesium calcite retains the calcite mineral structure, which is distinct from dolomite. Calcite in limestone is divided into low-magnesium and high-magnesium calcite, with the dividing line placed at a composition of 4% magnesium. However, the calcite in limestone often contains a few percent of magnesium. Dolomite, CaMg(CO 3) 2, is an uncommon mineral in limestone, and siderite or other carbonate minerals are rare. Limestone is composed mostly of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate ( CaCO 3). This limestone deposit in the karst of Dinaric Alps near Sinj, Croatia was formed in the Eocene. Limestone formations contain about 30% of the world's petroleum reservoirs. Limestone has numerous uses: as a chemical feedstock for the production of lime used for cement (an essential component of concrete), as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a soil conditioner, and as a popular decorative addition to rock gardens. Most cave systems are found in limestone bedrock. Limestone is exposed over large regions of the Earth's surface, and because limestone is slightly soluble in rainwater, these exposures often are eroded to become karst landscapes. Much dolomite is secondary dolomite, formed by chemical alteration of limestone. Most limestone was formed in shallow marine environments, such as continental shelves or platforms, though smaller amounts were formed in many other environments. Magnesian limestone is an obsolete and poorly-defined term used variously for dolomite, for limestone containing significant dolomite ( dolomitic limestone), or for any other limestone containing a significant percentage of magnesium.
The remaining carbonate rock is mostly dolomite, a closely related rock, which contains a high percentage of the mineral dolomite, CaMg(CO 3) 2.
Ībout 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life. 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 forms when these minerals precipitate out of water containing dissolved calcium. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of CaCO 3. Limestone ( calcium carbonate CaCO 3) is a type of carbonate sedimentary rock which is the main source of the material lime. Limestone outcrop in the Torcal de Antequera nature reserve of Málaga, SpainĬalcium carbonate: inorganic crystalline calcite or organic calcareous material
0 kommentar(er)
