Geoscience Reference
In-Depth Information
Conductivity (S/m)
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Conductors
Semiconductors
Insulators
Steel casing
Serpentine
Quartz, feldspars, pyroxenes, amphiboles, carbonates
Rock-forming minerals
Graphite
Native metals
Oxides
Metallic minerals
Sphalerite
Sulphides (except sph)
Air
Water
Ice
Pore contents
Hyper-saline
Fresh
Permafrost
Clay
Sand/gravel
Glacial sediments
Till
Duricrust
Regolith
Saprolite
Igneous/metamorphic
Crystalline rocks
Kimberlite
Ironstones/chert
Shale/mudrocks
Clastics
(graphitic)
Sedimentary rocks
Lignite/coal
Carbonates
Evaporites
10
-8
10
-7
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-6
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-5
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-4
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-3
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-2
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-1
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0
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Resistivity (Ω m)
Figure 5.12
Typical ranges in conductivity/resistivity for some common minerals, rock types and near-surface materials. Data compiled from
various published sources.
determining the electrical properties of individual minerals
is not critically important since this information cannot be
easily used to predict the properties of the mineralogical
aggregates
small quantities and exert very little in
uence over geo-
physical responses.
Common silicate and carbonate minerals are insulators,
although serpentine is more conductive.
•
that are bodies of mineralisation or
the
common rock types.
•
Metal sulphide minerals, with the notable exception of
sphalerite, are comparatively conductive, although indi-
vidual mineral species show large ranges in values.
Sphalerite is signi
cantly less conductive (more resistive)
than the other sulphide minerals, but the presence of
impurities may lower its resistivity to values comparable
to the others.
5.3.1.1
Properties of rocks and minerals
The following generalisations from
Fig. 5.12
are important
in terms of geophysical measurements for mapping and
exploration targeting:
Most materials in the geological environment are
semiconductors (see
Section 5.2.1.3
). Exceptions are the
highly conductive native metals, but they occur in very
•
Metal oxides are normally less conductive than the sul-
phides, and their range in conductivity overlaps that of
the main rock types, so the physical-property contrast
•
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