Ground Calcium Carbonate (GCC) or Limestone
Limestone is a common sedimentary rock composed primarily of the calcium carbonate mineral, calcite (CaCO3). Limestone constitutes approximately 10 percent of the sedimentary rocks exposed on the earth’s surface.
Limestone is formed either by direct crystallization from water (usually seawater
In the seas that covered much of the earth in earlier geological times lived many clams and other shelled forms of animal life. When the animals died, their shells, which are composed of calcium carbonate, fell to the bottom. Thick layers, which can be a mile or 2 kilometers deep, gradually were changed into rock. If the shells were only compressed, with little crystallization occurring, soft chalk results. The White Cliffs of Dover in England are made of this type of chalk. With more time and pressure, a coarsely crystallized rock can form, which is limestone. In limestone, most traces of the animal shells have disappeared.
Pure calcite, dolomite, and aragonite which are in the
Uses For Limestone
Limestone and marble are important building materials in most parts of the world. They are used as cut dimension stone (blocks and slabs) for
Either limestone or marble may be used as the basis for crushed or ground calcium carbonate. Ground calcium
Ground limestones are available in a broad range of sizes. When specifying the size of a ground calcium carbonate, either the top size (the size of the largest particles) or the median particle size (essentially the average) can be used. Commercially, top size is generally specified for coarser industrial minerals which may be as big as beach sand, which is 10 mesh or 2 millimeters or approximately 0.1 inch in size, or as fine as flour; which is 200 mesh, or 75 microns. Finely ground calcium carbonates can range down in particle size to just a few microns, 1 to 3, with the top size controlled for
Limestone color can range from brilliant white to light gray and chemical purity can range from only 80-90% calcium carbonate to well over 99.9% purity.
Calcium carbonate is not a particularly hard mineral, with pure calcite falling at about 3 on the Mohs scale of 1 (talc) to 10 (diamond). Silica impurities in the limestone can raise the hardness of some ground calcium carbonates to a Mohs value of 4. Calcium carbonate is subject to attack by acidic environments, which has led to the damage of limestone buildings and monuments by acid rain. For industrial uses, the effect of an acid can be somewhat reduced by treating the ground limestone powder with fatty acids to put a non-polar, organic material on the surface. Few industrial minerals can match GCC for its combination of properties and cost.
Specialty Minerals Limestone Products
Specialty Minerals Inc. (SMI) manufactures crushed and ground limestone products at two of the Performance Minerals plants. At Adams, MA and Lucerne Valley, CA, high brightness limestone from adjacent SMI mines are ground into products which range in size from ½” (1.7 cm) white decorative landscaping stones to fine, 2