Molybdite: properties and occurrences

Molybdite is the naturally occurring mineral form of molybdenum trioxide MoO3. It is a molybdenum trioxide, crystallizing in the orthorhombic system and usually occurring as flat yellow needles and plates forming encrustations. It occurs as yellow to greenish needles and crystallizes in the orthorhombic crystal system. It is a mineral, much of which is actually ferrimolybdite. It is an orthorhombic-dipyramidal mineral containing molybdenum and oxygen.

General Information

  • Category: Mineral
  • Formula: MoO3
  • Crystal system: Orthorhombic
  • Crystal class: Dipyramidal (mmm)
  • Color: Light greenish-yellow to nearly colorless.

“Molybdite occurs as yellow to greenish needles and crystallizes in the orthorhombic crystal system. It is a mineral, much of which is actually ferrimolybdite.”

Properties

Molybdite is a soft, graphitelike mineral, molybdenum sulfide, occurring in foliated masses or scales: the principal ore of molybdenum. Molybdenite crystals have the same hexagonal symmetry as those of tungstenite (tungsten disulfide). Both have layered structures and similar physical properties; the chief difference is the higher specific gravity of tungstenite.

Molybdite – a molybdenum trioxide

  • Crystal habit: Flattened needles or thin plates may occur in aggregates
  • Cleavage: Perfect on {100}, district on {001}
  • Tenacity: Flexible
  • Mohs scale hardness: 3 – 4
  • Luster: Adamantine
  • Streak: White
  • Diaphaneity: Transparent
  • Specific gravity: 4.72
  • Optical properties: Biaxial (+)

Occurrence

Molybdite was first described in 1854 for and occurrence in quartz veins in the Knöttel area of Krupka, Krušné Hory Mountains in the Ústí Region of Bohemia, Czech Republic.

It occurs in vein cavities and as coatings in molybdenite ore veins and quartz topaz greisens.

Associated minerals include molybdenite, betpakdalite, and quartz. A similar mineral ferrimolybdite is often misidentified as molybdite.