Powellite
Powellite is a rare molybdate mineral with the chemical formula CaMoO4. It is named after Professor John Wesley Powell, an American geologist and explorer. It is the calcium analogue of scheelite (CaWO4).
Occurrence and Formation:
Powellite is a secondary mineral typically found in the oxidized zones of molybdenum-bearing ore deposits. It commonly occurs as an alteration product of molybdenite (MoS2). It can also be found in some contact metamorphic environments and in association with other secondary minerals such as wulfenite, descloizite, and vanadinite.
Physical Properties:
Powellite is usually found as small, tetragonal crystals, sometimes as powdery coatings or massive aggregates. It exhibits a vitreous to adamantine luster and ranges in color from colorless to yellow, greenish-yellow, brown, or even gray. Its streak is white. Powellite has a Mohs hardness of 3.5-4 and a specific gravity of 4.2 to 4.5. It exhibits fluorescence under ultraviolet light, typically displaying a bright yellow or blue-white color. Its cleavage is distinct on {011} and imperfect on {112}. The mineral is brittle with a conchoidal fracture.
Identification:
Powellite can be identified by its crystal form, color, fluorescence, and association with other molybdenum minerals. Chemical tests can confirm the presence of calcium and molybdenum. X-ray diffraction is a definitive method for identification.
Uses:
Powellite is not a major ore mineral, but it can be collected by mineral enthusiasts. It may also be used as a minor source of molybdenum in some rare circumstances. Its fluorescent properties make it attractive to collectors.