Mendozite is a relatively rare sulfate mineral that forms in arid environments as a secondary product of sulfide oxidation. It typically appears as white, fibrous encrustations or efflorescent crusts and is highly soluble in water, requiring careful storage in low-humidity environments.
Is this mendozite?
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 mendozite with a known reference. Mendozite 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.
- 4Match the color rangeCompare against the expected color range: colorless, white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, massive, or encrusting.
Often confused with
Mendozite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Mendozite is noticeably harder (Mohs ~3 vs. 1.5-2).
How to tell apart: Mendozite is noticeably harder (Mohs ~3 vs. 1.5).
How to tell apart: Mendozite is noticeably harder (Mohs ~3 vs. 1.5).
Often found alongside mendozite
Minerals reported to co-occur with mendozite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaAl(SO₄)₂·11H₂O
- Mohs hardness
- ~3
- Density
- 1.730 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, massive, or encrusting
- Cleavage
- Good on {100}; indistinct on {001}; indistinct on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Rarely formed by oxidation of pyrite in reaction with clays; may occur in volcanic fumaroles
Where rockhounds find mendozite
Classic worldwide localities
- Eureka, St. Louis Co., and Fulton, Calloway Co., Missouri, USA
- Lanjarón mineral springs, Granada, Spain, Argentina
- Volcanoes on the Kamchatka Peninsula, Russia
Field-hunting tip
Where it forms: Rarely formed by oxidation of pyrite in reaction with clays; may occur in volcanic fumaroles. If you start seeing tamarugite in float, you are in the right ground. Typical habit: fibrous, massive, or encrusting. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify mendozite?+
Where is mendozite found?+
What rocks look like mendozite?+
What minerals are found with mendozite?+
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What is mendozite used for?+
Find mendozite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
