Carlsonite is a rare ammonium iron sulfate mineral that typically forms as delicate, efflorescent crusts or tiny tabular crystals. It is primarily known from specific volcanic environments where ammonium-rich gases interact with iron-bearing volcanic rocks. Due to its solubility and rarity, it is mostly sought after by serious mineral species collectors.
Is this carlsonite?
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 carlsonite with a known reference. Carlsonite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Carlsonite leaves a yellowish-white streak.
- 3Read the lusterHold the specimen under a strong light. Carlsonite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, greenish-yellow.
- 5Look at form & habitCrystal system: triclinic. Typical habit: tabular crystals, crusts, efflorescences.
Often confused with
Carlsonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Carlsonite leaves yellowish-white, Alunogen leaves white; luster reads vitreous on Carlsonite and silky on Alunogen.
How to tell apart: Streak differs, so Carlsonite leaves yellowish-white, Pickeringite leaves white; luster reads vitreous on Carlsonite and silky on Pickeringite.
Often found alongside carlsonite
Minerals reported to co-occur with carlsonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (NH₄)₅Fe³⁺₃(SO₄)₆·9H₂O
- Mohs hardness
- 2
- Density
- 2.16 g/cm³
- Colors
- Streak
- Yellowish-white
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Tabular Crystals, Crusts, Efflorescences
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Alteration Zones in Volcanic Rocks
- Typical price
- $50-200 for rare specimens
Where rockhounds find carlsonite
Classic worldwide localities
- Big Four Mountain, Washington, USA
Field-hunting tip
Look in hydrothermal alteration zones in volcanic rocks country, the host setting where carlsonite typically forms. If you start seeing alunogen, pickeringite, sulfur in float, you are in the right ground. Field specimens usually show a tabular crystals, crusts, efflorescences habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find carlsonite on the map
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