Even though no standard definition of the term “clay” is accepted by geologists, agronomists, engineers, and others, the term is generally well-understood by those who use it. Clay is an abundant, naturally occurring, fine-grained material composed predominantly of hydrous aluminum silicates.
Clay is not a single mineral, but a number of minerals. Clays fall into six general categories: kaolin, ball clays, fire clays, bentonite, common clays and Fuller’s earth. Clays are common all over the world. Some regions produce large quantities of specific types of clay. The United States is self-sufficient so it imports only small amounts of clay.
Description
Even though no standard definition of the term “clay” is accepted by geologists, agronomists, engineers, and others, the term is generally well understood by those who use it. Clay is an abundant, naturally occurring, fine-grained material composed predominantly of hydrous aluminum silicates.
Clay is not a single mineral, but a number of minerals. Clays fall into six general categories: kaolin, ball clays, fire clays, bentonite, common clays and Fuller’s earth. Clays are common all over the world. Some regions produce large quantities of specific types of clay. The United States is self-sufficient so it imports only small amounts of clay.
Relation to Mining
Common Clay Mining:
Typically, common clays and shales are mined from open pits, and these pits are located near the processing plants to minimize production costs. Usually both the raw material and the finished products are heavy and the profit margin is low, so production costs must be controlled. Most products made from these materials are processed and marketed in a similar manner to refractory clays. Common clays and shale require little beneficiation. Typically they are crushed or ground only before milling and extrusion. Physical contaminants such as concretions are removed by dry screening.
Uses
The United States both imports and exports clays and clay products. It is estimated that the United States consumes about 37.6 million tons of clays each year.
Ball clays are good quality clays used mostly in pottery but are also added to other clays to improve their plasticity. Ball clays are not as common as other clay varieties. One third of the ball clay used annually is used to make floor and wall tiles. It is also used to make sanitary ware, pottery, and other uses.
Bentonite is formed from the alteration of volcanic ash. Bentonite is used in pet litter to absorb liquids. It is used as a mud in drilling applications. It is also used in other industrial applications such as the “pelletizing” of iron ore.
Common clay is used to make construction materials such as bricks, cement, and lightweight aggregates.
Fire clays are all clays (excluding bentonite and ball clays) that are used to make items resistant to extreme heat. These products are called refractory products. Nearly all (81%) of fire clays are used to make refractory products.
Fuller’s earth is composed of the mineral palygorskite (at one time this mineral was called “attapulgite”). Fuller’s earth is used mostly as an absorbent material (74%), but also for pesticides and pesticide-related products (6%).
Kaolinite is a clay composed of the mineral kaolin. It is an essential ingredient in the production of high quality paper and some refractory porcelains.
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