coffinite

Coffinite is a hydrous uranium silicate mineral with the general formula USiO4·nH2O, in which uranium is in the tetravalent state. It is part of the silicate minerals that form in uranium-rich hydrothermal environments and can occur as crystals or as fine-grained masses. The mineral is typically described as having a brownish to yellow-brown color, with a vitreous to resinous luster. In well-formed crystals coffinite can be transparent to translucent; more commonly it appears as opaque to translucent crusts and aggregates. It is radioactive due to its uranium content.

Coffinite crystallizes in the tetragonal system and commonly forms prismatic to acicular crystals, or radiating and granular aggregates. Its physical properties reflect its uranium content, giving it a relatively high density for a silicate mineral and a hardness generally in the mid-range on the Mohs scale.

Occurrence and associations: Coffinite is found in uranium ore deposits, often in hydrothermal vein systems and in association with other uranium minerals such as uraninite, pitchblende, autunite, and torbernite. Notable localities include uranium-bearing districts in North America and elsewhere around the world, where it forms alongside other silicate and oxide phases.

Notes: As a uranium-bearing mineral, coffinite is radioactive and requires appropriate handling and safety precautions. Its identification relies on a combination of optical properties, chemical analyses, and crystallography, particularly its silicate composition and hydrous content.