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