Molybdenite Identification Guide

What Molybdenite Looks Like

Molybdenite (MoS2) is a soft, metallic sulfide that looks like a smear of pencil lead. It is silvery lead-gray with a strong, almost mirror-bright metallic luster on fresh cleavage faces. Crystals are hexagonal, forming thin tabular plates or six-sided "books," but it is far more common as foliated masses, scaly aggregates, or shiny flakes scattered through quartz.

• Color: lead-gray, sometimes with a bluish tint
• Luster: bright metallic, pearly on cleavage
• Habit: thin hexagonal plates, foliated/scaly masses, rosettes
• Feel: greasy, slippery; leaves a mark on your fingers

Step-by-Step Field ID Checklist

1. Check softness. Try to scratch it with a fingernail. Molybdenite is Mohs 1–1.5 and a nail (2.5) cuts it easily.
2. Test the feel. Rub a flake between your fingers — it feels greasy and slippery, like graphite.
3. Peel a flake. Cleavage flakes are flexible but NOT elastic; they stay bent after you flex them.
4. Do the streak test. Drag it on unglazed porcelain: molybdenite gives a greenish-gray streak. On paper it can look bluish-gray.
5. Heft it. It feels noticeably heavier than graphite (SG ~4.7 vs ~2.2).

Key Diagnostic Tests

• Hardness: 1–1.5; marks paper, cut by fingernail.
• Cleavage: perfect basal {0001}; splits into flexible sheets.
• Streak: greenish-gray (key diagnostic). On glazed porcelain a rubbed streak looks bluish-green.
• Specific gravity: 4.6–5.0 — surprisingly heavy for such a soft mineral.
• Not magnetic; no acid reaction.

Common Look-Alikes and How to Tell Them Apart

• Graphite: the classic confusion. Both are soft, gray, and greasy. Molybdenite is heavier (SG ~4.7 vs graphite ~2.2), has a faint bluish tint, and its streak on paper is bluish-gray/greenish, while graphite's is brownish-gray to black. Side by side, molybdenite is brighter and "whiter."
• Galena: also lead-gray and metallic but far harder feeling, brittle, shows cubic cleavage (right-angle steps), and is much denser (SG ~7.5).
• Hematite (specular): harder, gives a red-brown streak.

Where Molybdenite Is Found

Molybdenite is the world's main molybdenum ore. Look for it in:

• Porphyry copper-molybdenum deposits (disseminated flakes in altered granite)
• High-temperature quartz veins, greisens, and skarns
• Granite pegmatites

Classic localities include Climax and Henderson (Colorado), Questa (New Mexico), and many porphyry systems in the western Americas and Australia.

Forms, Treatments, and Field Notes

Molybdenite is almost never faked because it has little gem value, so most field confusion is natural mineral-on-mineral. Two practical habits help: it is rarely found as loose crystals — instead it occurs as bright flakes "frozen" in quartz, granite, or skarn, so train your eye to spot silvery glints in a matrix. It also commonly weathers to a yellow powdery coating of secondary molybdenum minerals (such as powellite or ferrimolybdite), and that pale yellow stain on rock is itself a useful prospecting clue that molybdenite is nearby.

A quick two-mineral test

If you suspect molybdenite versus graphite and have both in hand, weigh equal-sized chips — the molybdenite will feel distinctly heavier. Then rub each on white paper: molybdenite's mark has a faint greenish-bluish cast and a brighter sheen, while graphite is flat dull gray-black. Together with the higher density this is essentially diagnostic in the field without lab gear.