a. Symbol in structural petrology for the direction of tectonic transport,
similar to the direction in which cards might slide over one another.
Striations in a slickensided surface are parallel to direction a.
AGI
b. A crystallographic axis: In the isometric system each axis is
designated a; in hexagonal, tetragonal, and trigonal systems the nonunique
axes are a; in the orthorhombic system a is always shorter than b with c
either the longest or the shortest axis; in the monoclinic and triclinic
systems a may be determined by one of several conventions.
A Hawaiian term for lava consisting of a rough assemblage of clinkerlike
scoriaceous masses. It is contrasted with pahoehoe used to designate the
smoother flows. Pron. ah-ah. Fay; Hess
a. One of the three crystallographic axes used as reference in crystal
description. It is oriented horizontally, front to back.
b. One of the three reference axes used in describing a rock fabric
possessing monoclinic symmetry, such as progressive simple shear. The a
axis is the direction of tectonic transport, i.e., the direction of shear.
Syn:a direction
CF:b axis; c axis.
Excavations, either caved or sealed, that are deserted and in which
further mining is not intended and open workings that are not ventilated
and inspected regularly. Syn:abandoned mine
Federal Mine Safety
Abandonment of a mining claim may be by failure to perform work, by
conveyance, by absence, and by lapse of time. The abandonment of a mining
claim is a question of intent. To constitute an abandonment of a mining
claim, there must be a going away and a relinquishment of rights, with the
intention never to return and with a voluntary and independent purpose to
surrender the location or claim to the next comer. CF:forfeiture
In mineral processing, a porcelain jar used for laboratory batch grinding
tests in ceramic ware. Pryor, 1
An instrument to determine the index of refraction of a liquid between two
high-index glass prisms. CF:refractometer
The visibility of an object under the microscope is directly proportional
to the wavelength of light, and inversely to the aperture of lens.
Pryor, 3
A gear-driven tube mill supported on a pair of riding rings and
distinguished by an Archimedes spiral, through which the ore is fed and
discharged. Grinding is effected by flint pebbles fed into the mill.
See also:ball mill
A method of seismic surveying by which the effect of irregular weathering
thickness may be determined by a simple calculation from reciprocal
placement of shotholes and seismometers. The method was originally used to
solve refraction problems arising from irregularities in the top of the
high-velocity layer. AGI
Etching agent consisting of 10% chromium trioxide in water. Used in the
analysis of carbon steels. Bennett
A tetragonal mineral, K(UO2 )(AsO4 ).4H2 O ; in small
yellow crystals; in the Temple Mountains, UT.
a. The failure of a lens or mirror to bring the light rays to the same
focus. When aberration is due to the form of the lens or mirror, it is
called spherical aberration. When due to the different refrangibility of
light of different colors, it is called chromatic aberration. When present
in magnifiers it often causes inaccurate decisions as to flawlessness or
color of gems.
b. Distortion produced by a lens. It is spherical if a flat image appears
closer to the viewer in the middle than toward the edges of the field of
view. It is chromatic if the visible spectrum is spread to give both a red
and a blue image. CF:achromatic; aplanatic lens; aplanachromatic lens.
See also:chromatic aberration
A large, steep-sided vertical shaft opening at the surface of the ground.
AGI
See:solution breccia
A bulky machine that cuts a deep web of coal up to 6 ft (1.8 m) and is
used in cyclic mining in medium to thick seams. It runs on the floor of
the seam and does not require a prop-free front. It carries two horizontal
jibs, one cutting at floor level and the other at a height depending on
seam conditions. Nelson
A surveying instrument for taking levels up steep slopes; also used as a
clinometer. Hammond
A working place in a coal mine with adverse geological or other conditions
and in which the miner is unable to earn a wage, based on the pricelist,
equal to or above the minimum wage. A term generally associated with
stalls or pillar methods of working. Nelson
A device for assessing the wear resistance of surfaces. The specimen to be
tested is rubbed alternately by the flat faces of two weighted abrasive
wheels that revolve in opposite directions through frictional contact with
the specimen and exert a combined abrasive, compressive, and twisting
action twice in each revolution of the specimen holder. Osborne