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 — Carlsonite leaves yellowish-white, Alunogen leaves white; luster reads vitreous on Carlsonite and silky on Alunogen.
How to tell apart: Streak differs — 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 — that is 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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