Geology Reference
In-Depth Information
Gas chromatograph
A device in which a sample is vaporized and injected into the end
of a long chromatographic column. The sample is transported
through the column by the flow of an inert gas. Differences in
mass and chemical properties result in different arrival times at a
detector. Numerous detectors are available to measure different
properties of the exiting components.
Gas vents
Any opening in the earth
s surface where gas escapes into the
atmosphere. Vents transport heat energy from sources that may
include underground coal fires or near-surface molten rock.
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Ground fissures
A fracture on the earth
s surface through which gases and fluids
can be exchanged between the atmosphere and the subsurface.
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Inelastic scattering
The process by which an electron or a photon interacts with an
atom and kinetic energy is not conserved. As a result, the fre-
quency of the resultant scattered particle is shifted.
Infrared spectroscopy
The absorption measurement by a sample of infrared radiation for
the purpose of structural studies and compound identification.
Infrared radiation has wavelengths ranging from ~0.78 to
1000
m (10 - 6 m), between visible light and microwaves.
μ
Isostructural
A term that refers to minerals that have the same crystal structure
and some different kinds of atoms.
Micro-Dumas carbon - nitrogen method
A technique where a carbon- and/or nitrogen-bearing phase is
combusted at a high temperature and the product gases are ana-
lyzed using a chromatographic device.
Multichannel analyzer
A device that takes the very small voltage signal produced by a
detector, reshapes it into a Gaussian or trapezoidal shape, and
converts that signal into a digital signal.
Nanometer
A unit of length used to describe the scale of atoms. It is equal to a
one-billionth of a meter or 10 Å (10 - 9 m).
Nuclear magnetic resonance spectroscopy
A technique that measures the nearing neighbor environment of
atoms by placing a sample in a strong magnetic field. The spin of
the atom is tilted by an electromagnetic pulse and the relaxation of
the signal is recorded. The technique is applicable to odd integer
elements without large amounts of paramagnetic (i.e., Fe) com-
ponents. It is the same technology used in the medical field for
magnetic resonance imaging (MRI).
Optical spectroscopy
A technique that employs the scattering of light as it interacts with
a phase. Light can scatter, absorb, or fluoresce and be detected
electronically or with the human eye.
Powder Diffraction File
An electron database that holds diffraction patterns for inorganic
and organic compounds, including minerals.
Raman spectroscopy
An inelastic scattering technique that detects molecular vibrations.
It is useful for identifying bonds and compounds that vibrate in
the same range as infrared electromagnetic radiation.
Secondary electrons
Produced by incident electrons colliding with atoms in the
specimen, near enough to impart some of their energy to
lower energy electrons (usually in the K-shell of the atoms).
This causes a slight energy loss and path change in the incident
electrons and transition of electrons in the specimen atom. The
electrons that leave the surface of the specimen have a very
small kinetic energy (in the range of 2
-
50 eV), which are
attracted to a special detector.
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