A rock-statigraphic unit formerly classed as a formation but now called a
group because subdivisions of the unit are considered to be formations.
The part of a polariscope that receives the light after polarization and
exhibits its properties. In a petrographic microscope, it is the
polarizing mechanism (Nicol prism, Polaroid, etc.) that intersects the
light after it has passed through the object under study.
See also:polarizer
High-temperature, high-pressure remelting of preexisting rock to form
migma. CF:anatexis
The zone deep in the Earth's crust in which rock flowage takes place. The
term, originated in 1898 by Van Hise, is now little used.
CF:anamorphism
Intense metamorphism in the anamorphic zone in which rock flowage takes
place and simple minerals of low density are changed into more complex
ones of greater density by silication, decarbonization, dehydration, and
deoxidation. The term was originated by Van Hise in 1904.
CF:anamorphic zone; katamorphism. AGI
a. Pertaining to a network of branching and rejoining fault or vein
surfaces or surface traces. AGI
b. Said of the channel pattern of a braided stream. AGI
A tetragonal mineral, 4[TiO2 ] ; trimorphous with rutile and
brookite; brown, greenish-gray, or black; in hydrothermal veins around
granite pegmatites, as an alteration of titanium minerals, and as detrital
grains. Formerly called octahedrite. See also:octahedrite;
titanium dioxide; xanthitane.
See:anatexis
Melting of preexisting rock. This term is commonly modified by terms such
as intergranular, partial, differential, selective, or complete. Adj.
anatectic. CF:palingenesis; syntexis; anamigmatization. AGI
A clay mineral near kaolinite, but containing excess silica, probably as
interlayered sheets. Monoclinic. AGI; Dana, 4
A rapid plow for use on longwall faces. It is suitable for seams from 2 to
8 ft (0.6 to 3.9 m) thick, with reasonably good roof and floor. The plow
travels along the face at a speed of 75 ft/min (22.9 m/min) with a cutting
depth from 1-1/2 to 3 in (3.8 to 7.6 cm); the broken coal is loaded by the
plow-shaped body onto an armored conveyor. The machine can be operated
independently of the face conveyor. See also:plow-type machine;
Rehisshakenhobel. Nelson
Fillings of old workings in a mine, and said to carry gold of recent
deposition. This is a product that deposits in most of the old stopes
throughout the mine. In some instances, the whole stope for 20 ft (6.1 m)
wide is filled. It is apparently siliceous material with more or less
pyrite. Hess
That portion of any beam or structure designed to resist pulling out or
slipping of the beam or structure when subjected to stress. Nelson
a. A bolt with the threaded portion projecting from a structure, generally
used to hold the frame of a building secure against wind load or a machine
against the forces of vibration. Also called holding-down bolt; foundation
bolt. Hammond
b. A bolt or other device used to secure a diamond-drill base to a solid
foundation. It may or may not be threaded. Long
c. A lag screw used to anchor the drill base to a platform or sill.
Long
Means of fastening an explosive charge in a seismic shot hole to allow
several charges to be preloaded. At each stage the bottom charges are
fired first, the upper charges being held down by anchors. AGI
See:jack
See:stell prop
A mineral, SrCe(CO3 )2 (OH).H2 O ; in pegmatites.
An orthorhombic mineral, Al2 SiO5 ; trimorphous with kyanite
and sillimanite; Mohs hardness, 7-1/2; in aluminous shales and slates
subjected to high-temperature, low-stress metamorphism; transparent green
varieties used as gems. Syn:cross-stone
A trigonal mineral, Na2 Ca(UO2 )(CO3 )3 .6H
2 O ; bright yellow-green; secondary.
A widely used cutter loader in which the ordinary jib of the longwall coal
cutter is replaced by a shear drum which cuts a web from 16 to 22 in (40.6
to 55.9 cm) depending on its width. The machine travels on an armored
conveyor and requires a prop-free front for working. It shears the coal in
one direction and the front coal is loaded by a plow deflector, and then
returns along the face (without cutting) and loads the remainder of the
broken coal. The ordinary Anderton is suitable for coal seams more than 3
ft 6 in (1.1 m) thick. Nelson