Limestone pearls

Shell, coral, pearl (exoskeletons Limestone and/or Calcium carbonate... 

Eggshells are mostly calcium carbonate. Seashells, pearls, limestone, and chalk are also made of calcium carbonate. So are some of the most beautiful and complex places on earth—coral reefs. 

In order to produce the various glasses, soda ash, salt cake, and limestone or lime are required to flux the silica. In addition, there is a contribution of lead oxide, pearl (as potassium carbonate), saltpeter, borax, boric acid, arsenic trioxide, feldspar, and fluorspar, together with a great variety of metallic oxides, carbonates, and the other salts required for colored glass. 

Some of the Group IA and IIA metals are found in nature in the form of carbonates, silicates, nitrates, and phosphates. For example, calcium carbonate is one of the most important naturally occurring compounds, and it is found in several forms. The most common form of calcium carbonate is limestone, which is used extensively as a building stone as well as the source of lime. Other forms include chalk, calcite, aragonite, Iceland spar, marble, and onyx. Many other materials such as egg shells, coral, pearls, and seashells are composed predominantly of calcium carbonate. Thus, it is one of the most widely occurring compounds in nature. 

Calcium carbonate (KAL-see-um CAR-bun-ate) is one of the most common compounds on Earth, making up about 7 percent of Earth s crust. It occurs in a number of minerals and other natural materials, including aragonite, calcite, chalk, limestone, marble, marl, oyster shells, pearls, and travertine. Stalactites and stalagmites found in caves are made primarily of calcium carbonate. As indicated by the melting points of aragonite and calcite, the compound s physical properties may differ somewhat depending on its crystal form. It typically occurs as an odorless, tasteless white powder or colorless crystals. 

Calcium carbonate, CaC03 (also called calcite), is the principal mineral found in limestone, marble, chalk, pearls, and the shells of marine animals such as clams. 

The principal carbonate minerals are calcite (CaC03), magnesite (MgC03), dolomite [MgCa(C03)2], and siderite (FeC03). Calcite is the principal mineral in limestone and the main constituent of marble, chalk, pearls, coral reefs, and the shells of marine animals such as clams and oysters. Although CaC03 has low solubility in pure water, it dissolves readily in acidic solutions with evolution of CO2 ... 

The most important carbonate mineral is calcium carbonate, CaCOs. This substance occurs in beautiful colorless hexagonal crystals as the mineral calcite. Marble is a microcrystalline form of calcium carbonate, and limestone is a rock composed mainly of this substance. Calcium carbonate is the principal constituent also of pearls, coral, and most sea shells. It also occurs in a second crystalline form, as the orthorhombic mineral aragonite. 

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