Re-uploaded with new pictures where you can actually make out the colour
On all sides except for one it is a dark green-ish colour. The other side is kind of brown red-ish. All sides are completely smooth and I can hardly damage it with a knife. It looks as if it was damaged before tho on some parts (scratches on the surface, conchoidal dents where something appeared to have broken off). It's completely non-transparant an the colour is some kind of mat, dull green with a bit of a shine to it.
I tried to break it with a hammer but that hardly did any damage. Only one little chip broke off and left a conchoidal dent. on the bottom there a some white spots now because it was sitting on an non-smooth surface when I hit it.
My gf's cousin says it could be glass but I am not entirely sure since i cant break/destroy it. It's a bit heavier than expected
Close up of that brown/grey/black part. Some of it is dirt that i cant get off no matter what. The black part was set free when I hit it with the hammer and something broke off