Some unusual Chemistry notations

A member of the Math WG was on vacation and spotted some interesting
chemical notations while at a museum. This might be mineralogy-specific. I
invite everyone in the CG to add to the issue
<https://github.com/w3c/mathml/issues/93> their thoughts on them and/or
ways to speak the examples. Unfortunately, the examples are not accessible
because they are photos of the labels of the exhibits. If someone wants to
transcribe those, please feel free to do so and add them to the issue.

    Neil