Apjohnite is a secondary sulfate mineral that typically forms as delicate, fibrous efflorescences in mine workings and volcanic environments. Because it is highly soluble in water and dehydration-prone, collectors should store specimens in airtight containers to prevent them from crumbling into powder.
Is this apjohnite?
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 apjohnite with a known reference. Apjohnite sits at Mohs 1.5-2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Apjohnite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Apjohnite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, pale yellow, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, acicular, efflorescent, or crusts.
Often confused with
Apjohnite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside apjohnite
Minerals reported to co-occur with apjohnite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MnAl₂(SO₄)₄·22H₂O
- Mohs hardness
- 1.5-2
- Density
- 1.7-1.8 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, Acicular, Efflorescent, Or Crusts
- Cleavage
- Distinct On {110}
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Oxidized Ore Deposits and Coal Mine Workings
- Typical price
- $10-60 for small specimens
Where rockhounds find apjohnite
Classic worldwide localities
- South Africa
- United States
- Czech Republic
- Germany
Field-hunting tip
Look in oxidized ore deposits and coal mine workings country — that is the host setting where apjohnite typically forms. If you start seeing gypsum, jarosite, melanterite in float, you are in the right ground. Field specimens usually show a fibrous, acicular, efflorescent, or crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find apjohnite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
