Perhamite is a rare calcium aluminum silicate mineral often found as crusts or tiny, platy radial aggregates within cavities of granitic pegmatites. It is most famous for its discovery at the Perham Farm in Maine, where it occurs as a secondary mineral resulting from the alteration of other phosphate species. Collectors typically look for its characteristic pale, platy crystal clusters associated with other rare phosphate minerals.
Is this perhamite?
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 perhamite with a known reference. Perhamite sits at Mohs ~5, 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: dull, vitreous on cleavage surface.
- 4Match the color rangeCompare against the expected color range: light brown, white.
- 5Look at form & habitCrystal system: trigonal. Typical habit: platy.
Often confused with
Perhamite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Prehnite is the harder of the two (Mohs 6-6.5 vs. ~5); luster reads dull, vitreous on cleavage surface on Perhamite and vitreous, weak pearly on {001} on Prehnite.
How to tell apart: Luster reads dull, vitreous on cleavage surface on Perhamite and vitreous to pearly on Apophyllite.
Often found alongside perhamite
Minerals reported to co-occur with perhamite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₃Al₇.₇Si₃P₄O₂₃.₅(OH)₁₄.₁·8H₂O
- Mohs hardness
- ~5
- Density
- 2.64 g/cm³
- Colors
- Streak
- White
- Luster
- Dull, vitreous on cleavage surface
- Transparency
- Translucent to nearly opaque
- Crystal system
- Trigonal
- Crystal habit
- Platy
- Cleavage
- Imperfect on {0001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- As isolated masses in a vuggy, amblygonite-rich pegmatite (Bell Pit, Maine, USA)
Where rockhounds find perhamite
Classic worldwide localities
- Oxford Co., Maine, in the Bell Pit and Dunton mines, Newry, USA
- Emmons quarry, Greenwood, Maine, USA
- Ski Pike quarry, Cobble Hill, West Paris, Maine, USA
- Silver Coin mine, near Valmy, Iron Point district, Humboldt Co., Nevada, USA
- Tom's quarry, Kapunda, and the Moculta quarry, Mount Lofty Ranges, South Australia
Field-hunting tip
Where it forms: As isolated masses in a vuggy, amblygonite-rich pegmatite (Bell Pit, Maine, USA). If you start seeing siderite, wardite, amblygonite in float, you are in the right ground. Typical habit: platy. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify perhamite?+
Where is perhamite found?+
What rocks look like perhamite?+
What minerals are found with perhamite?+
What kind of rock does perhamite form in?+
What is perhamite used for?+
Find perhamite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
