Foggite is a rare phosphate mineral primarily known from the Big Fish River area in the Yukon. It typically occurs as small, delicate, white to colorless acicular or lath-like crystals associated with other rare secondary phosphates in vugs.
Is this foggite?
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 foggite with a known reference. Foggite sits at Mohs ~4, 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: white, colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular to lath-like crystals.
Often confused with
Foggite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside foggite
Minerals reported to co-occur with foggite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaAl(PO₄)(OH)₂·H₂O
- Mohs hardness
- ~4
- Density
- 2.78 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular to lath-like crystals
- Cleavage
- {010}, perfect; {100}, good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral, probably formed at < 300°C, in complex granite pegmatites
Where rockhounds find foggite
Classic worldwide localities
- Palermo #1 mine, near North Groton, Grafton Co., New Hampshire, USA
- Milgun Station, Western Australia
Field-hunting tip
Where it forms: A secondary mineral, probably formed at < 300°C, in complex granite pegmatites. If you start seeing carbonate-apatite, childrenite, whitlockite in float, you are in the right ground. Typical habit: acicular to lath-like crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify foggite?+
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What rocks look like foggite?+
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Find foggite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
