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, so 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, so 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, 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?+
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Find molysite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
