See:pleochroism
a. A minute zone of color or darkening surrounding and produced by a
radioactive mineral crystal or inclusion. AGI
b. Any of the concentrically colored aureoles in minerals--e.g., micas,
fluorite, and cordierite--centered by minute grains of minerals containing
radioactive elements, such as zircon and monazite. This discoloration
results from crystal structural radiation damage from alpha decay.
a. The property of exhibiting different colors in different directions by
transmitted polarized light. AGI
b. More precisely, the property of absorbing differently, light that
vibrates in different directions in passing through a crystal. If the
crystal is uniaxial the change of color is called dichroism; if the
crystal is biaxial, the change of color is called pleochroism. AGI
c. The property of birefringent crystals (minerals) to absorb various
wavelengths of light differentially depending on the vibration direction
of the light within the crystal. Thus a mineral displaying pleochroism
shows various colors or tints when it is traversed by plane polarized
light and the orientation of the crystal is varied with respect to the
plane of polarization. It is a common and diagnostic property of many
minerals, and is easily observed under the petrographic microscope or a
dichroscope. AGI
d. The capacity of strongly anisotropic minerals to change absorption
colors with changing electric vector in plane-polarized light; e.g., as
seen with a polarized-light microscope. Uniaxial minerals may be dichroic
and biaxial ones trichroic. Qualitative pleochroism is change of intensity
in the same color; quantitative pleochroism shows change of color with
change of orientation. Adj: pleochroic. CF:dichroism; trichroism.
Syn:polychroism
See:polymorphism
See:ceylonite
A fine grained intergrowth of kamacite and taenite.
A flexible cable having collective armor comprising stranded groups of
fine, galvanized, steel wires. BS, 13
A support composed of elastic materials that either yields to the roof
pressure, or permits the subsidence of the roof without the support being
completely destroyed and losing its significance. Stoces
Intense, small-scale folding. Adj: plicated. CF:crenulation
AGI
Eng. To dress down or remove loose stone from the roof or sides.
SMRB
A mineral, Ca5 H2 Si6 O18 .6H2 O(?) .
A mark made in a bit mold, bit die, or blank bit where a pip or hole is
drilled to receive or to encompass a diamond. Long
A large drawing machine by means of which stereoscopic pairs of vertical
photographs can be viewed in conjunction with their ground control points
and mechanically translated into accurate maps. Hammond
A scale used for setting off the lengths of lines in surveying.
a. In coal mining, a cutter loader with knives or blades, which is pulled
along the longwall face by a powerful chain. The broken coal is loaded
onto an armored flexible conveyor which, with the aid of hydraulic rams,
holds the plow up to the coal face and causes the knives to bite into the
coal as they are pulled along. The plow is a continuous mining machine.
See also:plow-type machine
b. Applied to V-shaped belt scrapers that are attached to the belt
conveyor frame and which press against the return belt. They are intended
to remove coal or other material that might stick to the return belt and
be crushed as the belt passes over the driving rolls or the return pulley.
Jones, 1
See:V-cut
a. A steel plate attached to the end of a cutter loader for deflecting cut
coal onto the face conveyor. Nelson
b. A device for removing or diverting the dust and dirt off a belt
conveyor and thus prevent it being carried back along the return belt.
Nelson
A high-tensile steel used in the manufacture of hoisting ropes.
Plows may be divided into two classes: (1) machines that peel the coal to
a depth of from 1 to 12 in (2.54 to 30.5 cm) by knives of various designs
and the cut coal is then loaded onto a heavy type scraper chain conveyor;
and (2) machines that peel a thin slice up to 2 in (5.1 cm) in thickness,
by knives attached to each end of a steel box, and the coal is dragged
along the face inside the box. From the aspect of speed of travel, plows
may be divided into: (1) slow-moving types of 10 to 20 ft/min (3.0 to 6.1
m/min), which remove a thicker slice; and (2) fast-moving types at about
80 ft/min (24.4 m/min), which take a relatively thin slice.
See also:Anbauhobel; continuous mining; Lobbe Hobel. Nelson
a. Describes the sudden jerking or plucking on heavy endless-rope haulage
when the rope again takes the load, following rope coils. Instead of
slipping smoothly sideways, the rope tends to stick until the pressure of
oncoming coils overcomes the friction; these slip suddenly, producing a
momentary slackening followed by a sudden jerk or pluck as the rope again
takes the load. This may loosen chains or clips and cause derailments and
runaway sets. Sinclair, 5
b. The disruption of blocks of rock by a glacier or stream.
Standard, 2
a. A watertight seal in a shaft formed by removing the lining and
inserting a concrete dam, or by placing a plug of clay over ordinary
debris used to fill the shaft up to the location of the plug.
BS, 10
b. See:hoisting plug
c. A steel cylinder placed inside the annular opening in a coring bit to
convert it for use as a noncoring bit. The face of the plug may or may not
be provided with serrations, inset diamonds, or other types of cutting
edges. Long
d. See:block
e. See:cartridge
f. A cylindrical piece of wood or an expandable metal apparatus placed in
a borehole to act as a base into which the drive wedge of a borehole
deflection device is driven.
g. Small wooden pin driven into a hole in the rock roof of a tunnel. The
axis of the tunnel is marked on such plugs by tacks, or by small iron
hooks from which a plummet lamp may be suspended for sighting upon.
Stauffer
h. To plug a well by cementing a block inside casing or capping the well
with a metal plate. Wheeler, R.R.
i. Any block installed within casing to prevent movement of fluids.
Wheeler, R.R.
j. A steel wedge used in quarrying dimension stone.
See:plug-and-feather method
k. A vertical, pipelike body of magma that represents the conduit to a
former volcanic vent. CF:neck