Since deposition, the organic matter of most oil
shales has been so changed over geological time
that little recognisable features remain. Microscopical
examination does not provide much help
for constitutional analysis and thus one cannot use
biological features as a basis for classification.
Tasmanite oil shale is a notable exception. The
kerogen is so sharply differentiated from the
mineral matrix that it can be largely separated
by mechanical means.
Tasmanite kerogen, when isolated, appears as
flattened discs, which, by various sectioning processes,
can be shown to have been nearly spherical
in shape before compaction. There has been a
great deal of argument as to the exact nature of
these dissemenules. The century-old suggestion,
originally rejected, that they are algal in origin
has now been generally accepted and it may be
taken that Tasmanites, as it occurs in oil shale,
represents the cyst stage of a peculiar alga belonging,
most likely, to the Chlorophyceae. The exact
relationship within the family is still uncertain.
Because of its discrete and peculiar structure, it
might be assumed that the organic matter of tasmanite
has a chemistry different from other algal
shales. This is true only in so far as the soluble
resin-like material is concerned, the pyrolysate
possesses a normal hydrocarbon chemistry, although
the non-hydrocarbon constituents are somewhat
more than usual. Infrared and other physical
methods of analysis support this hypothesis
