The quality of being opaque. See also:opaque
An amorphous or microcrystalline mineral, SiO2 .nH2 O ; may
be tridymite or cristobalite; has a varying proportion of water (as much
as 20% but commonly 3% to 9%); occurs in nearly all colors; transparent to
nearly opaque; typically shows a marked iridescent "play of color";
differs from quartz in being isotropic; has a lower refractive index than
quartz and is softer, more soluble, and less dense; generally occurs
massive and may be pseudomorphous after other minerals; deposited at low
temperatures from silica-bearing water; occurs in cracks and cavities of
igneous rocks, in flintlike nodules in limestones, in mineral veins, in
deposits of thermal springs, in siliceous skeletons of various marine
organisms (such as diatoms and sponges), in serpentinized rocks, in
weathering products, and in most chalcedony and flint. The transparent
colored varieties exhibiting opalescence are valued as gemstones.
Syn:opalite
A milky or somewhat pearly appearance or luster of a mineral, such as that
shown by opal and moonstone. CF:play of color
a. Any of several minerals related to or resembling opal; e.g., a
pale-blue to bluish-white opalescent or girasol corundum, or a brecciated
impure opal pseudomorphous after serpentine. AGI
b. An earthy form of gypsum. AGI
c. A rock with a groundmass or matrix consisting of opal. adj. Resembling
opal, esp. in appearance; e.g., opaline feldspar (labradorite) or opaline
silica (tabasheer). AGI
See:opal
Silicified wood. See also:wood opal
Said of a material that is impervious to visible light or has metallic
luster. CF:transopaque; translucent; transparency; transparent; opacity
Attritus that is opaque in thin sections. Syn:opaque-durit
Tomkeieff
Refers to coal material of which the most prominent and important
constituent is opaque matter and also referred to as opaque matrix, black
fundamental matter or matrix and residuum. IHCP
See:opaque-attrite
A working in which excavation is performed from the surface. Commonly
called open pit. See also:bench; quarry. CF:strip mine
Syn:opencut; opencut mine. Webster 3rd
A mining method consisting of removing the overlying strata or overburden,
extracting the coal, and then replacing the overburden. When the overlying
material consists of earth or clay it can be removed directly by scrapers
or excavators, but where rock is encountered it is necessary to resort to
blasting to prepare the material into suitable form for handling by the
excavators. See also:strip mining
See:opencast
See:opencast; strike working.
In mineral dressing, a flow line in which the solid particles pass from
one appliance to the next without being screened, classified, or otherwise
checked for quality; no fraction is returned for retreatment.
Pryor, 2
A grinding mill without classifiers. Nelson
Shaft timbering with cribs alone, placed at intervals. Fay
a. To increase the size of a shaft when it intersects a drift so as to
form a puddle wall behind the sets of timber.
b. Open pit; surface working in which the working area is kept open to the
sky. See also:opencast
An excavation for removing minerals which is open to the weather.
See also:opencast
See:surface mining; openpit mining.