[jnurmine]

Also not a mineral expert -- I didn't really understand anything from Wikipedia's description, "monoclinic with space group I2/c, and is isostructural with...".

But since it's naturally occuring, perhaps even existing bismuth mines elsewhere have more of these rare grains, if one knows how to look for them.

[gus_massa]

The atoms in crystasl are organized in small repeated "cells". Monoclinic means that each cell has the shape of a small slanted brick https://en.wikipedia.org/wiki/Monoclinic . Isostructural means that other minerals have the atoms in the same arrangement.

Space group I2/c is more detailed info about where the atoms are in the small cells/slanted brick. I have no idea what it exactly means. It's a name very specific to cristalographers, sometimes the same group has a different name in math or phisics, and sometimes nobody has a similar problem to be interested in that group. You can try to take a look at https://en.wikipedia.org/wiki/Crystallographic_point_group Aparently there are 6 (six!) naming conventions, but I can't find I2/c to save my life. And Google didn't help either. (I'd glad if anyone can give more info.)

[jnurmine]

This was very helpful, thanks!

It's often the very domain-specific language that hides (at least on the surface) rather simple concepts. I do appreciate how confusing software engineering terminology must seem to outsiders... zombies, chicken bits, duck typing, core affinity, etc.

[gilleain]

So a physics stack exchange question (https://physics.stackexchange.com/questions/221440/space-gro...) led me to a paper (https://nvlpubs.nist.gov/nistpubs/jres/107/4/j74mig.pdf) that discusses the difference between C-centered (base-centered) cells and I-centered (body centered cells).

Long story short, I think I2/c is conventionally C2/c - https://www.globalsino.com/EM/page1891.html

[bcraven]

If you think Wikipedia is hard to parse, try the womderful site Mindat:

https://www.mindat.org/min-46909.html