Molysite is a rare iron chloride mineral typically found as a sublimation product around volcanic fumaroles. It is extremely deliquescent, meaning it rapidly absorbs moisture from the air and dissolves into a liquid, making it a challenging mineral to preserve in a dry collection.
Is this molysite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch molysite with a known reference. Molysite sits at Mohs 1.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Molysite leaves a yellow streak.
- 3Read the lusterHold the specimen under a strong light. Molysite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, reddish-yellow, red.
- 5Look at form & habitCrystal system: trigonal. Typical habit: crusts, efflorescences, stalactitic.
Often confused with
Molysite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Erythrosiderite is the harder of the two (Mohs 2.5 vs. 1.5); streak differs — Molysite leaves yellow, Erythrosiderite leaves yellowish-orange.
How to tell apart: Halite is the harder of the two (Mohs 2.5 vs. 1.5); streak differs — Molysite leaves yellow, Halite leaves white.
Often found alongside molysite
Minerals reported to co-occur with molysite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeCl₃
- Mohs hardness
- 1.5
- Density
- 2.33 g/cm³
- Colors
- Streak
- Yellow
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Crusts, Efflorescences, Stalactitic
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Volcanic Fumaroles
- Typical price
- $50-300 per specimen
Where rockhounds find molysite
Classic worldwide localities
- Mount Vesuvius, Italy
- Etna, Sicily
- Various fumarolic environments
Field-hunting tip
Look in volcanic fumaroles country — that is the host setting where molysite typically forms. If you start seeing hematite, sulphur, halite in float, you are in the right ground. Field specimens usually show a crusts, efflorescences, stalactitic habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify molysite?+
Where is molysite found?+
How much is molysite worth?+
Is molysite safe to handle?+
What rocks look like molysite?+
What minerals are found with molysite?+
What kind of rock does molysite form in?+
What is molysite used for?+
Find molysite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
