Geology Reference
In-Depth Information
Oxy-anion
A polyatomic anion incorporating oxygen
(and/or hydroxide) alongside another element. e.g.
nitrate NO
3
-
. Alternatively known as oxo-anions.
Polybasic
Synonym of
polyprotic.
Polymer
Material whose molecules are built up from
a series of identical smaller units. Thus polyethylene
consists of chains of ≤80 ethylene (ethene, C
2
H
4
) mol-
ecules bonded together.
Polyprotic
Describes an acid whose formula con-
tains more than one hydrogen atom, and whose
dissociation therefore produces more than one
hydrogen ion (Appendix B).
Polymorph
One of several alternative crystal struc-
tures that a given substance can adopt.
Positron (
β
+
)
Anti-matter counterpart of an
electron
.
Potential energy
The energy a body possesses by
virtue of its position in a force field such as gravity.
ppm
See
parts per million
.
Precipitate, precipitation
Formation of insoluble
solid from solution, or formation of liquid droplets
from vapour. Requires solution or vapour to be
supersaturated
(Chapter 4).
Precise
Describes a measurement that is subject to
only a small
random error
.
Precision
The magnitude of the
random error
associated with a measurement. (Confusingly, 'high-
precision' describes a measurement that has a low
random error.)
Primitive
A material that has undergone little or no
differentiation
or
fractionation
.
Product
A chemical species formed by a chemical
reaction (appearing on the right-hand side of the
written reaction).
Prograde
(of metamorphic reactions) Proceeding to
higher grade, or higher temperature.
Proton (p
+
)
Positively charged massive nuclear
particle.
Pseudo-binary, pseudo-ternary
System which for
practical purposes approximates to a two-compo-
nent (binary) system, but which in certain details
exhibits more complex behaviour, e.g. crystallizing
phases whose compositions lie outside the system.
Likewise 'pseudo-ternary'.
Partial (vapour) pressure (
p
i
)
The pressure in Pa
exerted individually by one volatile component
i
in
a gas or other phase.
Partition coefficient
K
i
A
See Box 9.1.
Parts per million (ppm)
Unit of (low) concentration
of an element (not oxide). 1 ppm = 1 g per 10
6
g = 1
μ
g
per g = 1 mg per kg. 10
3
ppm = 0.1%. In gas mixtures,
'ppm' usually refers to parts per million by volume
(ppmv).
Peridotite
Rock type comprising more than 40%
Mg-rich olivine (together with other Mg-rich miner-
als such as pyroxene) making up the bulk of the
Earth's mantle.
Perthite
The name for a potassium feldspar crystal
containing
exsolution lamellae
of sodium feldspar
- see Figures 2.6b and 2.7.
Petroleum
Term embracing all naturally occurring
liquid and gaseous hydrocarbon deposits.
pH
See Appendix B.
Phase
(chemical usage) A part of a
system
occupying
a specific volume and having uniform
1
physical and
chemical characteristics which distinguish it from all
other parts of the system. For example, olivine crys-
tals, melt and gas bubbles in a crystallizing magma
constitute three distinct phases.
Phase boundary
Line or surface on a phase diagram
marking the limit of
P-T-X
stability of a particular
phase or assemblage.
Photodissociation
Break-up of a molecule caused by
a high-energy
photon
(e.g. Equation 3.8).
Photon
Quantum of light. Behaves in some respects
like a particle.
Polarizability
Susceptibility of a substance to
polari-
zation
on the atomic or molecular scale: a measure
of how easily
electron
density can be deformed in an
electric field.
Polarization
(a) Attraction of negative charge toward
one side of an atom, ion or bond, leaving the other
side with a net positive charge. (b) A light beam
whose electric vector vibrates only in one plane is
said to be plane-polarized.
Quantum number
A number - usually an integer -
whose multiple values (0, 1, 2, etc.) identify alterna-
tive electron orbitals/waveforms/stationary states
in an atom (Table 5.3) or the harmonics of any stand-
ing wave (see Figure 5.2).
Radioactive
Undergoing spontaneous nuclear decay.
1
Or continuously varying, as in a
zoned
mineral crystal.
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