powellite

Powellite is a mineral species with the chemical formula CaMoO4, a calcium molybdate. It is isostructural with scheelite (CaWO4), sharing the tetragonal crystal system and a similar calcium-centered framework in which molybdenum substitutes for tungsten.

Powellite forms in hydrothermal ore deposits, particularly those containing molybdenum and tungsten. It is commonly found in association with minerals such as calcite, quartz, fluorite, and scheelite. The mineral typically occurs as transparent to translucent yellow crystals, often prismatic or tabular, with a vitreous luster. Crystal sizes range from millimeters to a few centimeters in well-formed specimens.

In terms of properties, powellite is moderately hard and relatively dense for a non-metallic mineral, with a Mohs hardness around 4 to 5 and a fairly high specific gravity. It is usually yellow to orange-yellow in color, though color can vary slightly depending on impurities or alteration.

Occurrence and distribution: powellite has been reported in various molybdenum- and tungsten-bearing hydrothermal deposits worldwide. It is usually considered an accessory mineral rather than a primary ore, with molybdenum typically sourced from other minerals such as molybdenite.

Significance: powellite is of interest to mineral collectors and researchers for its relationship to scheelite and for providing information about the geochemical conditions in molybdenum-rich hydrothermal systems.