A name given to the X direction as pencilled on Z sections of unfaced
quartz and whose position is determined by X-ray measurements or etching.
The name is also given to the artificial prism face (parallel to 1120)
thus located, and produced by sawing the section in the YZ plane. Also
applied to the natural growth faces on faced raw quartz crystals.
Am. Mineral., 2
The frequency of free oscillation of a system. For a
multiple-degree-of-freedom system, the natural frequencies are the
frequencies of the normal modes of vibration. Hy
natural frequency of a foundation
The frequency of free vibration of a complete soil-foundation oscillating
system. This frequency must differ distinctly from that of any machinery
carried by the foundation if resonance is to be avoided. Hammond
natural frequency vibrating conveyor
A vibrating conveyor in which the rate of free vibration of the trough on
its resilient supports is approx. the same as the rate of vibration
induced by the driving mechanism.
natural gamma radiation detector
This is a type of sensor that measures bursts of high-energy
electromagnetic waves that are emitted spontaneously by some naturally
occurring radioactive elements, such as potassium-40, thorium-232, and
uranium-238, that are commonly present in shales and clays. Mowrey
A process whereby gamma rays naturally emitted by formations traversed by
a borehole are measured. A tool containing a radiation detector is lowered
into the borehole and gamma ray measurements are transmitted to the
Earth's surface. The signals are utilized to produce a record of gamma
rays detected in correlation with the depth of the detector in the
borehole. The record thus obtained in the form of a curve indicating
relative number per unit of time of natural gamma rays at different
depths, is a conventional natural gamma-ray log, sometimes simply called a
gamma-ray log. Williams
A mixture of the low-molecular-weight paraffin series hydrocarbons
methane, ethane, propane, and butane, with small amounts of higher
hydrocarbons; also frequently containing small or large proportions of
nitrogen, carbon dioxide, and hydrogen sulfide, and occasionally small
proportions of helium. Methane is almost always the major constituent.
Natural gas accompanying petroleum always contains appreciable quantities
of ethane, propane, butane, as well as some pentane and hexane vapors, and
is known as wet gas. Dry gas contains little of these higher hydrocarbons.
The exact composition of natural gas varies with locality. The heating
value of natural gas is usually over 1,000 Btu/ft3 unless
nitrogen or carbon dioxide are important components of the gas.
See also:gas; sour gas. CCD, 2
A vitreous, amorphous, inorganic substance that has solidified from magma
too quickly to crystallize. Granitic or acid natural glass includes pumice
and obsidian; an example of a basaltic natural glass is tachylite.
AGI
A logarithm with e as a base. Webster 3rd
A term used by foundrymen to refer to a sand that, as mined, contains
sufficient bonding material for molding purposes. Osborne
a. In iron mining, the term given to naturally occurring high-grade iron
ore; consists of: (1) soft ore, such as porous hematite and limonite
(goethite) with minor magnetite and manganese oxides; and (2) hard ores,
such as compact, fine-grained, steel-gray hematite, specular hematite,
magnetite, or martite. Syn:direct shipping ore
b. Iron ore that contains moisture, in contrast to "dry ore" that has been
dried but not calcined. USBM, 7
c. A term used in the U.S. Lake Superior mining district to indicate iron
ore formed by natural processes, as distinguished from iron ore products
(such as pellets) produced artificially from hard, low-grade ores of the
taconite type. Published prices for natural ores from this district
usually specify iron content as "natural," meaning that the analysis is
based on gross weight including moisture. Syn:lump ore; silicious ore;
high-silica ore; wash ore; heavy-media ore; manganiferous ore;
natural ore concentrate; lean ore; paint-rock ore;
Mesabi non-Bessemer ore.
See:natural ore
Brownish paperlike deposit formed from the filaments of Conferva.
Tomkeieff
See:resin
Sand derived from a rock, in which the grains separate along their natural
boundaries. This includes unconsolidated sand or a soft sandstone where
little pressure is required to separate the individual grains.
Osborne
Applied to a drawing made to equal vertical and horizontal scales.
Hammond
The maximum angle at which loose material in a bank or spoil heap will
stand without slipping. See also:angle of rest; angle of slide.
Nelson
In mine ventilation, a practice that allows the airflow to divide among
the branches of its own accord and without regulation, in inverse relation
to the resistance of each airway. CF:controlled splitting
Hartman, 2
The failure of the skin rock of an excavation by crushing, shear, or
plastic flow. It can occur on free surface rock with explosive force.
See also:arching
a. In a mine, air returning from the workings to the surface via the
upcast shaft can be of a higher temperature than the air in the downcast
shaft because of heat added to the ventilation current from the strata
exposed in the mine. Thus, even in a mine with the fan stopped, the upcast
air density is less than the downcast air density. This lack of balance in
the two vertical air columns produces a pressure difference across the
shaft bottom doors known as natural ventilating pressure.
Roberts, 1
b. The ventilating pressure that produces natural ventilation.
BS, 8