a. Any thin section used in microscopic analysis. AGI
b. A polished section. AGI
A collective term for small motions in the Earth that are unrelated to an
earthquake and that have a period of 1.0 to 9.0 s. They are caused by a
variety of natural and artificial agents, esp. atmospheric events.
Syn:seismic noise
An instrument for observing the behavior of roof strata and supports. The
device is inserted in 4-ft (1.2-m) long 1-1/2-in (3.8-cm) diameter holes,
drilled at selected points, for listening to subaudible vibrations which
are known to precede rock failure. Nelson
See:microseism.
The number of microseisms per unit of time. Issacson
Area in which an earthquake is registered by instruments only.
Schieferdecker
An apparatus for indicating the direction, duration, and intensity of
microseisms. Also called microseismograph. Standard, 2
Calcite matrix in limestones, occurring as uniformly sized and generally
loaf-shaped crystals ranging from 5 mu m to more than 20 mu m in diameter.
AGI
Said of the spherulitic texture of an igneous rock that is distinguishable
only with the aid of a microscope, owing to the small size of the
spherules. Also, said of a rock having such texture. AGI
Microscopic scratch developed on the polished surface of a rock or mineral
as a result of abrasion. AGI
a. Structural features of rocks that can be discerned only with the aid of
the microscope. AGI
b. The structure of polished and etched metals as revealed by a microscope
at a magnification greater than 10 diameters. ASM, 1
A type of grain boundary indicating differential solution between two
minerals and characterized by fine interpenetrating teeth; often marked by
a little opaque material. See also:stylolite
The thin vitrainlike bands present in clarain, having a maximum thickness
of about 1/10 in (2.5 mm) with a tolerance of 1 mm, and a minimum
thickness of 0.05 mm (50 mu m). AGI
One-millionth of a volt; 10-6 V; symbol, mu V. Crispin
One-millionth of a watt; symbol, mu W. Webster 3rd
See:foyaite; nepheline syenite.
A mountain range that extends parallel to the continental margins in
mid-ocean in both the North and South Atlantic Oceans. It rises 6,000 ft
above the ocean floor and surfaces as the Azores, Ascension Island, Saint
Helena, and Tristan da Cunha islands. AGI
Pertaining to a segment of geologic time intermediate between Late and
Early, or to rocks intermediate between Upper and Lower. Thus, rocks of
the Middle Jurassic Series were formed during the Middle Jurassic Epoch.
CF:Upper; Lower.
A machine cut in the midsection of a coal seam; sometimes adopted in thick
seams (over 4 ft or 1.2 m) with a layer of dirt or inferior coal in the
middle. A middle cut would be made with a turret coal cutter.
See also:bottom cut; top cut. Syn:intermediate cut
A stratum of rock dividing or separating two seams or beds of coal.
Fay
See:center prop