Search results
Results from the WOW.Com Content Network
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO 3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratch hardness comparison. Large calcite crystals are used in optical equipment, and limestone composed ...
Calcite alabaster, harder than the gypsum variety, was used in ancient Egypt and the wider Middle East (except Assyrian palace reliefs), and also in modern times. It is found as either a stalagmitic deposit from the floor and walls of limestone caverns , or as a kind of travertine , similarly deposited in springs of calcareous water.
The origin of the carbonate-rich septaria is still debated. One possibility is that dehydration hardens the outer shell of the concretion while causing the interior matrix to shrink until it cracks. [ 36 ] [ 34 ] Shrinkage of a still-wet matrix may also take place through syneresis , in which the particles of colloidal material in the interior ...
Construction marble is a stone which is composed of calcite, dolomite or serpentine that is capable of taking a polish. [20] More generally in construction , specifically the dimension stone trade, the term marble is used for any crystalline calcitic rock (and some non-calcitic rocks) useful as building stone.
During diagenesis of carbonate sediments, significant chemical and textural changes take place. For example, aragonite is converted to low-magnesium calcite. Diagenesis is the likely origin of pisoliths, concentrically layered particles ranging from 1 to 10 mm (0.039 to 0.394 inches) in diameter found in some limestones. Pisoliths superficially ...
Crystal structure of calcite. Calcium carbonate is a chemical compound with the chemical formula Ca CO 3.It is a common substance found in rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skeletons and pearls.
Originating from the Persian word for the gem, lāžward, [1] lapis lazuli is a rock composed primarily of the minerals lazurite, pyrite and calcite. As early as the 7th millennium BC, lapis lazuli was mined in the Sar-i Sang mines, [2] in Shortugai, and in other mines in Badakhshan province in modern northeast Afghanistan. [3]
Molar tooth structures are ribbon-like veins and nodules of calcite that are found widespread in Precambrian carbonate sedimentary rocks between approximately 2600 to 570 million years ago. [1] Their mechanism for formation remains debated, with hypothesis including the generation of methane gas within sediments, [ 2 ] [ 3 ] pumping of water ...