Halotrichite is a secondary sulfate mineral that typically forms as delicate, silky, fibrous efflorescences or crusts in the vicinity of weathering sulfide deposits. Due to its high water content and solubility, specimens should be stored in a dry, sealed environment to prevent dehydration and crumbling.
Is this halotrichite?
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 halotrichite with a known reference. Halotrichite 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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless, green, gray white, yellow, white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: encrustations, fibrous.
Often confused with
Halotrichite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside halotrichite
Minerals reported to co-occur with halotrichite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeAl₂(SO₄)₄·22H₂O
- Mohs hardness
- 1.5
- Density
- 1.89 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Encrustations, fibrous
- Cleavage
- On {010}, poor
- Rarity
- Common
- Uses
- Collector
- Host rock
- As efflorescences in weathering sulfide deposits and oxidizing pyritic coals, with persistent accumulations in arid climates; as a precipitate around volcanic fumaroles and hot springs
Where rockhounds find halotrichite
1 mapped spotsClassic worldwide localities
- Alum Mountain district, Grant Co., New Mexico, USA
- Sulfur Hole prospect, near Borate, about 10 km northeast of Yermo, Calico Hills, San Bernardino Co., and at hot springs around Mt. Lassen, Shasta Co., California, USA
- Dexter No. 7 mine, Calf Mesa, San Rafael district, Emery Co., Utah, USA
- Solfatara di Pozzuoli, Campi Flegrei, near Naples, Campania, Italy
- Középső-György mine, Recsk, Mátra Mountains, Hungary
- Falun, Sweden
Field-hunting tip
Where it forms: As efflorescences in weathering sulfide deposits and oxidizing pyritic coals, with persistent accumulations in arid climates; as a precipitate around volcanic fumaroles and hot springs. If you start seeing melanterite, copiapite, gypsum in float, you are in the right ground. Typical habit: encrustations, fibrous. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Missouri. Start trip planning there.
Common questions
How do you identify halotrichite?+
Where is halotrichite found?+
Can I find halotrichite in the United States?+
What rocks look like halotrichite?+
What minerals are found with halotrichite?+
What kind of rock does halotrichite form in?+
What is halotrichite used for?+
Find halotrichite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
