A habit with slender crystals radiating out from a central point.

 

Crystals originating from a common point that also form a distinctive pattern that points in an outwardly direction.

 

Steeply inclined rectangular or cylindrical opening used for ventilation or for conveying ore, miners or equipment. The slope is generally 45 degrees but varies up to 90 degrees. Also called a chute.

 

A secondary or tertiary inclined opening, driven to connect levels, usually driven in a downward direction, and used for haulage.

 

The restoration of land and environmental values to a surface mine site after the coal is extracted. Reclamation operations are usually underway as soon as the coal has been removed from a mine site. The process includes restoring the land to its approximate original appearance by restoring topsoil and planting native grasses and ground covers.

 

The proportion or percentage of coal or ore mined from the original seam or deposit.

 

A nonvolatile combustion product of the oxidation of coal or coal refuse. Most commonly applied to material resulting from in situ, uncontrolled burning of coal or coal refuse piles. It is similar to coal ash.

 

A specimen which lacks aesthetic qualities, suitable for study, but not display.

 

Restoring an old mining site to a natural state.

 

A habit showing large rounded shapes, between botryoidal and mammillary in size.

 

A luster similar to the resin exuded from plants.

 

A habit made up of slender crystals crossing each other in a network pattern.

 

A system of robbing pillars in which the robbing line, or line through the faces of the pillars being extracted, retreats from the boundary toward the shaft or mine mouth.

 

The air or ventilation that has passed through all the working faces of a split.

 

A crystal having six sides, each of which forms a parallelogram.

 

To extract pillars of coal previously left for support.

 

(1) A high place in the bottom or a low place in the top of a mine passage, (2) a local thickening of roof or floor strata, causing thinning of a seam.

 

The stratum of rock or other material above a coal seam; the overhead surface of a coal working place. Same as "back" or "top."

 

A long steel bolt driven into the roof of underground excavations to support the roof, preventing and limiting the extent of roof falls. The unit consists of the bolt (up to 4 feet long), steel plate, expansion shell, and pal nut. The use of roof bolts eliminates the need for timbering by fastening together, or "laminating," several weaker layers of roof strata to build a "beam."

 

A mine cave-in especially in permanent areas such as entries.

 

A screw- or pump-type hydraulic extension post made of steel and used as temporary roof support.

 

The sinking, bending, or curving of the roof, especially in the middle, from weight or pressure.

 

Unbalanced internal forces in the roof or sides, created when ore is extracted.

 

A method of underground mining in which approximately half of the coal is left in place to support the roof of the active mining area. Large "pillars" are left while "rooms" of coal are extracted.

 

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