Aphthitalite is a rare sulfate mineral that typically forms as white or colorless crusts around volcanic fumaroles or within saline evaporite deposits. Collectors should handle these specimens with care, as they are highly water-soluble and must be stored in dry, climate-controlled environments to prevent degradation.
Is this aphthitalite?
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 aphthitalite with a known reference. Aphthitalite sits at Mohs 3, 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 to resinous.
- 4Match the color rangeCompare against the expected color range: blue, colorless, green, gray, gray blue.
- 5Look at form & habitCrystal system: trigonal. Typical habit: encrustations, massive.
Often confused with
Aphthitalite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside aphthitalite
Minerals reported to co-occur with aphthitalite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (K,Na)₃Na(SO₄)₂
- Mohs hardness
- 3
- Density
- 2.66-2.71 g/cm³
- Streak
- White
- Luster
- Vitreous to resinous
- Transparency
- Transparent to opaque
- Crystal system
- Trigonal
- Crystal habit
- Encrustations, massive
- Cleavage
- On {1010}, fair; on {0001}, poor
- Fluorescence
- Weak yellow under SW UV; butter yellow under LW UV
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- An uncommon incrustation around volcanic fumaroles; a component of evaporite deposits; in guano deposits, then typically ammonian
Where rockhounds find aphthitalite
1 mapped spotsClassic worldwide localities
- Searles Lake, San Bernardino Co., California, USA
- Carlsbad potash district, Eddy Co., New Mexico, USA
- Kilauea, Hawaii, USA
- Mount St. Augustine volcano, Alaska, USA
- Campania, at Vesuvius and Monte Somma, in the Cesano geothermal field, east of Lake Bracciano, Lazio, and on Etna, Sicily, Italy
- Douglashall, near Westeregeln, Saxony-Anhalt, Germany
Field-hunting tip
Where it forms: An uncommon incrustation around volcanic fumaroles; a component of evaporite deposits; in guano deposits, then typically ammonian. If you start seeing thénardite, jarosite, sylvite in float, you are in the right ground. Typical habit: encrustations, massive. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in California. Start trip planning there.
Common questions
How do you identify aphthitalite?+
Where is aphthitalite found?+
Can I find aphthitalite in the United States?+
What rocks look like aphthitalite?+
What minerals are found with aphthitalite?+
What kind of rock does aphthitalite form in?+
What is aphthitalite used for?+
Find aphthitalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
