Coffinite is a uranium bearing silicate mineral: U(SiO4)1-x(OH)4x.

It is a glass-like black material, dark brown or pale-brown in color, possibly with grayish black streaks. It is named for American geologist Reuben Clare Coffin. It has molecular weight 327.71 daltons. It has no good cleavages and a brittle fracture. It is black with a black streak. The hardness of coffinite is between 5 and 6.