Molybdenum ochre

Molybdite or molybdenum ochre forms orthorhombic crystals, and occurs with molybdenite, from which it is probably derived. It consists essentially of the trioxide MoOg, but analysis has shown that its composition is probably expressed by the formula Fe203-3Mo03.7jH20 it being, in fact, a hydrated ferric molybdate. The sample examined was of a yellow colour, possessed a fibrous structure and a silky lustre, and was pleochroic. 

Chromium, 122 ppm of the earth s crustal rocks, is comparable in abundance with vanadium (136 ppm) and chlorine (126 ppm), but molybdenum and tungsten (both 1.2 ppm) are much rarer (cf. Ho 1.4 ppm, Tb 1.2 ppm), and the concentration in their ores is low. The only ore of chromium of any commercial importance is chromite, FeCr204, which is produced principally in southern Africa (where 96% of the known reserves are located), the former Soviet Union and the Philippines. Other less plentiful sources are crocoite, PbCr04, and chrome ochre, Cr203, while the gemstones emerald and ruby owe their colours to traces of chromium (pp. 107, 242). 

Another uranium phosphate mineral, lermontovite, has been described by Soboleva and Pudovkina. This mineral occurs as botryoidal aggregates of radial fibrous needles. The formula is apparently U3(P04)4-6H20 with some substitution of Ca and RE for the U. The material is poorly characterized. It is associated with molybdenum sulphate, marcasite, hydrous silicates and thallium ochre . This phase requires more careful characterization. 

A secondary deposit, associated with the weafriering of molybdenum ores is molybdic ochre and consists primarily of molybdite, M0O3. 

Ilsemannite Lead molybdate Ochre Wulfenite Blue carmine Molybdate orange Molybdate red Molybdenum blue Molybdenum green Bersch (1901) 239 Colour Index (1971) 77769 Harley (1982) 59 Salter (1869)171-172... 

---