I suppose this isn't really such a bad word. The only really horrible thing about it is the spelling.
You say it gang. In fact, the alternative spelling of it is gang. So, let's face it, gangue only exists to be ugly and to confuse and upset people.
The meaning of gangue is nothing much to do with the sorts of gangs we usually think about, though. Gangue is valueless and undesirable material found in metal-bearing rock. It's quite often small bits of quartz.
Stuff like the white bits of this:
So, gangue. Another autological word, I'd say.
Word Not To Use Today: gangue. This word comes from the French, and before that from the German Gang, which means vein of metal.