Both have 'cryptomorphic' types which are similar in composition but in which no felspar has crystallized.

Yikes! I was to be alone with the smacker and my non-smiling sister. After all the joy with my two boys in our family, I was to be left alone with the two gloomies. Well, I guess I will have to find something else to keep me busy.

Really syncophant stuff, but it may help. It's gratis in any case.

But black holes are infamously invisible, so they have to be observed indirectly.