Coffinite is a uranium-bearing silicate mineral with formula: U(SiO<sub>4</sub>)<sub>1−x</sub>(OH)<sub>4x</sub>.
It occurs as black incrustations, dark to pale-brown in thin section. It has a grayish-black streak. It has a brittle to conchoidal fracture. The hardness of coffinite is between 5 and 6.
It was first described in 1954 for an occurrence at the La Sal No. 2 Mine, Beaver Mesa, Mesa County, Colorado, US, X-ray powder patterns from samples of coffinite allowed geologists to classify it as a new mineral in 1955. Stieff et al. analyzed coffinite using the x-ray powder diffraction technique and determined that it has a tetragonal structure. which is significant because of uranium's use in nuclear energy. Sedimentary deposits contain the most radioactive samples,