I found this half submerged in Skegness beach, UK, on the sea front.
Lustre: Dull matte
Texture: Very grainy
Weight: 921 grams. Seems heavy
Size: 6 x 4 inches or 120 x 150mm MOH scale: 2.5 scratched with fingernail
I think I can rule out coal: it's too heavy and doesn't leave any black marks. It seems very grainy where coal is flat and grainless.