sulfides
Molybdenite
MoS2
- Crystal system
- hexagonal
- Hardness
- 1–1.5 on the Mohs scale
- Lustre
- metallic
- Colour
- Lead grey with a blue tinge
- Where it forms
- In porphyry deposits and high-temperature veins, usually with quartz.
- Chiefly from
- Colorado, United StatesChileChinaNorway
Why it is that colour
Metallic. It is so soft it marks paper, and so slippery it feels greasy.
Safety
Relatively low toxicity as sulfides go, and molybdenum is an essential trace element. It is extremely soft and leaves marks on everything, and the dust should not be inhaled. Standard precautions: no powdering, no water, no mouth.
Where it comes from
Chiefly a by-product of copper porphyry mining in Chile and the United States, plus primary mines such as Climax in Colorado. Molybdenum goes into high-strength steel.
Historical use
For centuries molybdenite, graphite and galena were confused with one another — all grey, soft and metallic — and the name comes from the Greek for lead. They were separated in 1778 by Carl Wilhelm Scheele.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
Worth knowing
Molybdenite has a second life in modern physics. Its structure is a stack of atom-thick sheets held together weakly, and single sheets can be peeled off in the same way that graphene is peeled from graphite — but unlike graphene, single-layer molybdenum disulfide is a semiconductor with a usable band gap, which makes it a serious candidate for atomically thin transistors.
It is also a dry lubricant, used where oil would fail, including in space. The same weak bonding between sheets that lets it be peeled apart lets it slide.
Identity checked against IMA-CNMNC master list, June 2025.