Fraipontite is a rare zinc-rich member of the serpentine group typically found in the oxidation zones of zinc-bearing ore bodies. It usually occurs as delicate, platy, or earthy masses, often displaying a soft pearly luster that distinguishes it from common smithsonite.
Is this fraipontite?
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 fraipontite with a known reference. Fraipontite sits at Mohs 3.5-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white to pale green.
- 3Read the lusterHold the specimen under a strong light. Luster: silky.
- 4Match the color rangeCompare against the expected color range: bluish, yellowish white, light green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: encrustations, fibrous, porcelainous.
Often confused with
Fraipontite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads silky on Fraipontite and vitreous, porcelaneous, earthy on Chrysocolla.
How to tell apart: Luster reads silky on Fraipontite and vitreous, may be pearly on Smithsonite.
How to tell apart: Luster reads silky on Fraipontite and vitreous, subpearly, adamantine, rarely silky on Hemimorphite.
Often found alongside fraipontite
Minerals reported to co-occur with fraipontite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Zn,Al)₃(Si,Al)₂O₅(OH)₄
- Mohs hardness
- 3.5-4
- Density
- 3.08-3.10 g/cm³
- Streak
- White to pale green
- Luster
- Silky
- Transparency
- Opaque to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Encrustations, fibrous, porcelainous
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In oxidized zinc-bearing mineral deposits
Where rockhounds find fraipontite
Classic worldwide localities
- Silver Bill mine, Gleeson, Cochise Co., Arizona, USA
- Blanchard mine, Socorro Co., New Mexico, USA
- Mohawk mine, San Bernardino Co., California, USA
- Original locality not known with certainty, but thought to be one of the mines of Vieille-Montagne (Altenberg), near Moresnet, Belgium
- Tsumeb, Namibia
- Laurium, Greece
Field-hunting tip
Where it forms: In oxidized zinc-bearing mineral deposits. If you start seeing smithsonite, gebhardite, willemite in float, you are in the right ground. Typical habit: encrustations, fibrous, porcelainous. Train your eye for that shape before scanning the outcrop.
Common questions
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Find fraipontite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
