Molybdenite
MoS₂ · Hexagonal
Molybdenite is the primary ore of molybdenum and looks almost exactly like graphite. Weight is the practical field test: molybdenite is more than twice as dense, and the difference is obvious once you hold both.
Properties
- Mohs hardness
- 1–1.5
- Streak
- gray, black
- Lustre
- metallic
- Colour
- Lead gray with a distinct blue cast that graphite lacks.
- Cleavage
- Perfect basal cleavage into flexible, inelastic flakes.
- Fracture
- Flaky
- Specific gravity
- 4.6–4.8 (water = 1)
- Magnetism
- Not magnetic
- Acid test
- No reaction
- UV
- Not fluorescent
Tests that confirm molybdenite
- Greasy feel like graphite, but roughly twice as heavy.
- Leaves a greenish-gray streak on paper; graphite's is neutral black.
- Extremely soft — a fingernail marks it.
What molybdenite gets confused with
Each of these is settled by one test. Run that test first.
Density. Molybdenite feels heavy for something this soft; graphite feels like nothing.
Where it is found
Porphyry copper and molybdenum deposits, and in some granite pegmatites and quartz veins.
Is it worth anything?
Modest collector value for good hexagonal plates.