19
History and Terminology
The second recognized type in this category is grahamite, which is very much like gilsonite in
external characteristics but is distinguished from the latter by its black streak, relatively high fixed
carbon value (35%–55%), and high temperature of fusion, which is accompanied by a characteristic
intumescence. The undifferentiated term grahamite must be used with caution; similarities in the
characteristics of samples from different areas do not necessarily imply any chemical or genetic
relationship.
A third but rather broad category of asphaltite includes a group of bituminous materials
known as glance pitch, which physically resemble gilsonite but have some of the properties of
grahamite. They have been referred to as intermediates between the two, although the possibility
exists that they are basically different from gilsonite and may represent something between bitumen
and grahamite.
Asphaltoids are a further group of brown to black, solid bituminous materials of which the members are differentiated from the asphaltites by their infusibility and low solubility in carbon disulfide. These substances have also been designated asphaltic pyrobitumen, as they decompose on
heating into bitumen-like materials. However, the term pyrobitumen does not convey the impression
intended; thus, the members of this class are referred to as asphaltoids since they closely resemble
the asphaltites.
Pyrobitumen is a naturally occurring solid organic substance that is distinguishable from bitumen (q.v.) by being infusible and insoluble. When heated, however, pyrobitumen generates, or transform into, bitumen-like liquid and gaseous hydrocarbon compounds. Pyrobitumen may be either
asphaltic or nonasphaltic. The asphaltic pyrobitumens are derived from petroleum, are relatively
hard, and have a specific gravity below 1.25. They do not melt when heated but swell and decompose (intumesce).
There is much confusion regarding the classification of asphaltoids, although four types are
recognized, elaterite, wurtzilite, albertite, and impsonite, in order of increasing density and fixed
carbon content. In fact, it is doubtful that the asphaltoid group can ever be clearly differentiated
from the asphaltites. It is even more doubtful that the present subdivisions will ever have any real
meaning, nor is it clear that the materials have any necessary genetic connection. Again, caution
should be exercised in the use of the names, and due care should be applied to qualification of the
particular sample.
1.4.9 BItumInous roCk And BItumInous sAnd
Bituminous rock and bituminous sand (see also bitumen, page 17) are those formations in which
the bituminous material is found as a filling in veins and fissures in fractured rocks or impregnating relatively shallow sand, sandstone, and limestone strata. The deposits contain as much as 20%
bituminous material, and if the organic material in the rock matrix is bitumen, it is usual (although
chemically incorrect) to refer to the deposit as rock asphalt to distinguish it from bitumen that is
relatively mineral free. A standard test (ASTM D4) is available for determining the bitumen content
of various mixtures with inorganic materials, although the use of the word bitumen as applied in
this test might be questioned and it might be more appropriate to use the term organic residues to
include tar and pitch.
If the material is of the asphaltite-type or asphaltoid-type, the corresponding terms should be
used: rock asphaltite or rock asphaltoid.
Bituminous rocks generally have a coarse, porous structure, with the bituminous material in the
voids. A much more common situation is that in which the organic material is present as an inherent
part of the rock composition insofar as it is a diagenetic residue of the organic material detritus that
was deposited with the sediment. The organic components of such rocks are usually refractory and
are only slightly affected by most organic solvents.
A special class of bituminous rocks that has achieved some importance is the so-called oil shale.
These are argillaceous, laminated sediments of generally high organic content that can be thermally
History and Terminology
The second recognized type in this category is grahamite, which is very much like gilsonite in
external characteristics but is distinguished from the latter by its black streak, relatively high fixed
carbon value (35%–55%), and high temperature of fusion, which is accompanied by a characteristic
intumescence. The undifferentiated term grahamite must be used with caution; similarities in the
characteristics of samples from different areas do not necessarily imply any chemical or genetic
relationship.
A third but rather broad category of asphaltite includes a group of bituminous materials
known as glance pitch, which physically resemble gilsonite but have some of the properties of
grahamite. They have been referred to as intermediates between the two, although the possibility
exists that they are basically different from gilsonite and may represent something between bitumen
and grahamite.
Asphaltoids are a further group of brown to black, solid bituminous materials of which the members are differentiated from the asphaltites by their infusibility and low solubility in carbon disulfide. These substances have also been designated asphaltic pyrobitumen, as they decompose on
heating into bitumen-like materials. However, the term pyrobitumen does not convey the impression
intended; thus, the members of this class are referred to as asphaltoids since they closely resemble
the asphaltites.
Pyrobitumen is a naturally occurring solid organic substance that is distinguishable from bitumen (q.v.) by being infusible and insoluble. When heated, however, pyrobitumen generates, or transform into, bitumen-like liquid and gaseous hydrocarbon compounds. Pyrobitumen may be either
asphaltic or nonasphaltic. The asphaltic pyrobitumens are derived from petroleum, are relatively
hard, and have a specific gravity below 1.25. They do not melt when heated but swell and decompose (intumesce).
There is much confusion regarding the classification of asphaltoids, although four types are
recognized, elaterite, wurtzilite, albertite, and impsonite, in order of increasing density and fixed
carbon content. In fact, it is doubtful that the asphaltoid group can ever be clearly differentiated
from the asphaltites. It is even more doubtful that the present subdivisions will ever have any real
meaning, nor is it clear that the materials have any necessary genetic connection. Again, caution
should be exercised in the use of the names, and due care should be applied to qualification of the
particular sample.
1.4.9 BItumInous roCk And BItumInous sAnd
Bituminous rock and bituminous sand (see also bitumen, page 17) are those formations in which
the bituminous material is found as a filling in veins and fissures in fractured rocks or impregnating relatively shallow sand, sandstone, and limestone strata. The deposits contain as much as 20%
bituminous material, and if the organic material in the rock matrix is bitumen, it is usual (although
chemically incorrect) to refer to the deposit as rock asphalt to distinguish it from bitumen that is
relatively mineral free. A standard test (ASTM D4) is available for determining the bitumen content
of various mixtures with inorganic materials, although the use of the word bitumen as applied in
this test might be questioned and it might be more appropriate to use the term organic residues to
include tar and pitch.
If the material is of the asphaltite-type or asphaltoid-type, the corresponding terms should be
used: rock asphaltite or rock asphaltoid.
Bituminous rocks generally have a coarse, porous structure, with the bituminous material in the
voids. A much more common situation is that in which the organic material is present as an inherent
part of the rock composition insofar as it is a diagenetic residue of the organic material detritus that
was deposited with the sediment. The organic components of such rocks are usually refractory and
are only slightly affected by most organic solvents.
A special class of bituminous rocks that has achieved some importance is the so-called oil shale.
These are argillaceous, laminated sediments of generally high organic content that can be thermally