Coffinite
Coffinite is a uranium silicate mineral with the chemical formula U(SiO4)1-x(OH)4x. It is a relatively common secondary uranium mineral found in a variety of geological settings, typically associated with hydrothermal uranium deposits and altered sedimentary rocks.
Properties:
- Chemical Composition: Primarily uranium silicate, with hydroxyl groups partially substituting for silicate.
- Crystal System: Tetragonal
- Habit: Typically occurs as fine-grained, sooty or earthy masses. Individual crystals are rare and usually microscopic.
- Color: Black, grayish-black, or dark brown.
- Streak: Dark brown to black
- Luster: Dull, earthy, or pitchy.
- Hardness: 5-6 (Mohs scale)
- Density: 5.1 - 5.2 g/cm3
- Radioactivity: Strongly radioactive due to its uranium content.
Occurrence:
Coffinite is found as a secondary mineral formed by the alteration of primary uranium minerals such as uraninite. It's often found in sandstone-type uranium deposits, roll-front deposits, and in hydrothermal vein deposits. Associated minerals commonly include uraninite, pitchblende, quartz, clay minerals, and other secondary uranium minerals like uranophane and autunite.
Identification:
Coffinite is often difficult to identify visually due to its fine-grained nature and dark color. Identification typically relies on X-ray diffraction or other analytical techniques. Its strong radioactivity can be a clue to its presence.
Uses:
Coffinite is primarily of interest as a uranium ore mineral. Its presence can indicate the potential for economically viable uranium deposits.
Safety Considerations:
Due to its high radioactivity, coffinite should be handled with care. Proper safety precautions, including limiting exposure and wearing appropriate protective equipment, should be followed when working with samples containing coffinite.