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. Streak: tan.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: yellow, orange-brown.
- 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.
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)₅Fe₃O(SO₄)₆·7H₂O
- Mohs hardness
- 2
- Density
- 2.167 g/cm³
- Colors
- Streak
- Tan
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Tabular crystals, crusts, efflorescences
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Formed by a natural fire in oil-bearing shale exposed along a cliff
Where rockhounds find carlsonite
Classic worldwide localities
- Big Four Mountain, Washington, USA
Field-hunting tip
Where it forms: Formed by a natural fire in oil-bearing shale exposed along a cliff. If you start seeing anhydrite, boussingaultite, gypsum in float, you are in the right ground. Typical habit: tabular crystals, crusts, efflorescences. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify carlsonite?+
Where is carlsonite found?+
What rocks look like carlsonite?+
What minerals are found with carlsonite?+
What kind of rock does carlsonite form in?+
What is carlsonite used for?+
Find carlsonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
