Check curtain- Sheet of brattice cloth hung across an airway to control the passage of the air current.

Chock- Large hydraulic jacks used to support roof in longwall and shortwall mining systems.

Clay vein- A body of clay-like material that fills a void in a coal bed.

Cleat- The vertical cleavage of coal seams. The main set of joints along which coal breaks when mined.

Clean Air Act Amendments of 1990�C A comprehensive set of amendments to the federal law governing the nation's air quality. The Clean Air Act was originally passed in 1970 to address significant air pollution problems in our cities. The 1990 amendments broadened and strengthened the original law to address specific problems such as acid deposition, urban smog, hazardous air pollutants and stratospheric ozone depletion.

Clean Coal Technologies�C A number of innovative, new technologies designed to use coal in a more efficient and cost-effective manner while enhancing environmental protection. Several promising technologies include: fluidized-bed combustion, integrated gasification combined cycle, limestone injection multi-stage burner, enhanced flue gas desulfurization (or "scrubbing"), coal liquefaction and coal gasification.

Coal- A solid, brittle, more or less distinctly stratified combustible carbonaceous rock, formed by partial to complete decomposition of vegetation; varies in color from dark brown to black; not fusible without decomposition and very insoluble.

Coal dust- Particles of coal that can pass a No. 20 sieve.

Coal Gasification�C The conversion of coal into a gaseous fuel.

Coal mine- An area of land and all structures, facilities, machinery, tools, equipment, shafts, slopes, tunnels, excavations, and other property, real or personal, placed upon, under, or above the surface of such land by any person, used in extracting coal from its natural deposits in the earth by any means or method, and the work of preparing the coal so extracted, including coal preparation facilities. British term is "colliery".

Coal reserves- Measured tonnages of coal that have been calculated to occur in a coal seam within a particular property.

Coal washing�C The process of separating undesirable materials from coal based on differences in densities. Pyritic sulfur, or sulfur combined with iron, is heavier and sinks in water; coal is lighter and floats.

Coke�C A hard, dry carbon substance produced by heating coal to a very high temperature in the absence of air.

Collar- The term applied to the timbering or concrete around the mouth or top of a shaft. The beginning point of a shaft or drill hole at the surface.

Colliery- British name for coal mine.

Column flotation

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