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 2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Mendozite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Mendozite typically shows a vitreous luster.
- 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.
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
- 2.5
- Density
- 1.76 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, Massive, Or Encrusting
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Sulfide Ore Deposits
- Typical price
- $20-100 for small specimens
Where rockhounds find mendozite
Classic worldwide localities
- San Juan Province, Argentina
- Chile
- California, USA
Field-hunting tip
Look in oxidized zones of sulfide ore deposits country — that is the host setting where mendozite typically forms. If you start seeing alunogen, pickeringite, gypsum in float, you are in the right ground. Field specimens usually show a fibrous, massive, or encrusting habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find mendozite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
