A ventilation system is composed of a fan and a set of connected ducts. In
a mine ventilation system, mine openings comprise the ducts. At a given
air density and with the fan operating at constant speed, there is only
one head and quantity of airflow that can result. This is an equilibrium
condition and is known as the operating point of the system.
Hartman, 2
In crystallography, the rotation, reflection, or inversion of an attribute
of a crystal structure to complete its symmetry. CF:element
Figures given on flowsheets to indicate quantities passing various points
in plant per unit time, taking account of fluctuations in the rate of
supply and composition (as to size and content of impurity), as follows:
(1) design capacity, the rate of feed, defined by limits expressing the
extent and duration of load variations, at which specific items of plant
subject to a performance guarantee must operate continuously and give the
guaranteed results on a particular quality of feed; (2) peak design
capacity, a rate of feed in excess of the design capacity, which specific
items of plant will accept for short periods without fulfilling the
performance guarantees given in respect of them; and (3) mechanical
maximum capacity, the highest rate of feed at which specific items of
equipment, not subject to performance guarantees, will function on the
type and quality of feed for which they are supplied. BS, 5
Operative temperature is that temperature of an imaginary environment in
which, with equal wall (enclosing areas) and ambient air temperatures and
some standard rate of air motion, the human body would lose the same
amount of heat by radiation and convection as it would in some actual
environment at unequal wall and air temperatures and for some other rate
of air motion. Strock, 2
A recrystallized metamorphic rock composed of calcite and serpentine,
commonly formed by dedolomitization of a siliceous dolostone. Some
ophicalcites are highly veined and brecciated and are associated with
serpentinite. AGI
A group of mafic and ultramafic igneous rocks ranging from spilite and
basalt to gabbro and peridotite, including rocks rich in serpentine,
chlorite, epidote, and albite derived from them by later metamorphism,
whose origin is associated with an early phase of the development of a
geosyncline. The term was originated by Steinman in 1905. AGI
A general term for diabases that have retained their ophitic structure
although the pyroxene is altered to uralite. The term was originated by
Palasson in 1819. AGI
Applied to a texture characteristic of diabases or dolerite in which
euhedral or subhedral crystals of plagioclase are embedded in a mesotasis
of pyroxene crystals, usually augite. Also said of a rock with such a
texture. CF:poikilitic
Optical properties apparently at variance with optical rules, such as:
anisotropy in isotropic minerals, such as birefringent diamond; biaxiality
in uniaxial minerals, such as quartz; and erratic variation in
birefringence near optical absorption bands--e.g., some epidote minerals.
Crystalline calcite so clear that it has value for optical purposes; e.g.,
polarizers. Syn:Iceland spar
An optical device that enables a theodolite to be accurately positioned
over or under a survey station. Also called optical plummet (undesirable
usage). BS, 7
The designation as to whether optically positive or optically negative;
said of minerals. Fay
In optical mineralogy, any of the following: indices of refraction,
birefringence, optic sign, axial angles, extinction angles, and dispersion
of a nonopaque mineral. In ore microscopy (mineragraphy), any of the
reflectances and anisotropy of opaque minerals.
See also:reflected-light microscope
The study of the behavior of light in crystals. Hurlbut
Constructive interference of monochromatic light; e.g., labradorescence in
plagioclase, fire in opal. See also:diffraction
Glass or other surface rendered truly planar. Pryor, 3
Carefully made glass of great uniformity and usually special composition
to give desired transmission, refraction, and dispersion of light.
CCD, 2
The determination of optical properties of minerals for the purpose of
characterization and identification. See also:index of refraction
Any of several effects of a substance upon light. Refractive index, double
refraction, (and its strength, birefringence), dispersion, pleochroism,
and color are gemmologically the most important optical properties.
A type of pyrometer that measures high temperature by comparing the
intensity of light of a particular wavelength from the hot material with
that of a filament of known temperature. It is used to determine the
temperature of incandescent lavas. See also:pyrometer
When a translucent crystal is viewed under microscope, light travels
through the mineral at a speed which corresponds with its refractive
index, as this is affected by the crystal planes. A uniaxial crystal has a
negative optical sign when the velocity of its extraordinary ray exceeds
that of the ordinary ray and vice versa. Calcite is negative; quartz
positive. For biaxial crystals, the three principal directions of
vibration are mutually at right angles. Pryor, 3