This pyrite cube is either still in the matrix it hailed from or has been glued onto the rock. It does come out of material like this so it could be genuine. When I went looking I found a lot of these, all around the £15 mark, all similar. I suspect some kind of human interference.

Anyway, this is a really cool addition to any crystal collection. The perfect cube is a characteristic fools gold colour. The matrix some kind of sand or clay stone.