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Rock and gem collectors are familiar with geodes - rocks with hollow centers that often
contain beautiful crystals inside. However, the geodes in Tyson’s Creek, Illinois (USA),
often contain smatterings of crude oil and tar. Scientists (who have also found them in
California, Iowa, and El Salvador) still cannot explain the presence of petroleum in
these rocks.
Geodes are normally created by minerals that form inside the rock’s cavities. Growing
inward, it is thought that their cores are sealed from the outside. However, oil and tar
are formed by decomposing organic, living matter under high temperature and pressure.
According to researchers, these two processes do not occur together. Apparently, however,
the geodes have accomplished the improbable.
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