Impact breccias and asteroids

I was interested to find this in a museum in Manchester. I had come across breccias before as being rock shattered when a fault forms and then hot mineral rich water flows into the joins. The water evaporates and the mineral cements the fragments. The classic sign of this is when the bits have sharp corners so no rounding has been caused by transport. It had never occurred to me that a big meteorite or asteroid strike could do the same. So how do you tell the two types of breccia apart? Is it in a known impact crater? Impact can produce so much heat that the minerals can turn to glass which might be observed. Is there too much iridium isotope that has to have come from outer space?