First, what it isn't; it isn't oil and it isn't shale. The rock
is a marlstone rich in calcium carbonate that is intermediate
between mudstone and limestone. The black stuff is kerogen, a
precursor to oil. Because kerogen is a mixture of organic
material, rather than a specific chemical; it cannot be given a
chemical formula. Indeed its chemical composition can vary
distinctively from sample to sample. Kerogen from the Green
River Formation oil shale deposit of Colorado contains elements
in the proportions Carbon 215 : Hydrogen 330 : Oxygen 12 :
Nitrogen 5 : Sulfur In order to convert kerogen to oil it must
be heated to high temperatures. Nature converts kerogen into oil
by burying the rock to the point where the temperature and
pressure is sufficient to do the job. Colorado's oil shale was
never buried deeply enough to reach the conditions of converting
the kerogen to oil. Historically, humans have tried to do this
artificially by bringing oil shale to the surface and roasting
it in kilns. Today, instead of