Foshagite is a rare calcium silicate mineral typically found as delicate, fibrous, or acicular white masses in contact metamorphic zones. It is most famous for its occurrences in the limestone quarries of Crestmore, California, where it forms in skarn deposits alongside other calcium-rich minerals.
Is this foshagite?
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 foshagite with a known reference. Foshagite 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. Foshagite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Foshagite typically shows a silky luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, gray.
- 5Look at form & habitCrystal system: triclinic. Typical habit: fibrous, acicular, radiating masses.
Often confused with
Foshagite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Wollastonite is the harder of the two (Mohs 4.5-5 vs. 3); luster reads silky on Foshagite and vitreous on Wollastonite.
How to tell apart: Xonotlite is the harder of the two (Mohs 6-6.5 vs. 3); luster reads silky on Foshagite and pearly on Xonotlite.
How to tell apart: Pectolite is the harder of the two (Mohs 4.5-5 vs. 3); luster reads silky on Foshagite and vitreous to silky on Pectolite.
Often found alongside foshagite
Minerals reported to co-occur with foshagite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₄Si₃O₉(OH)₂
- Mohs hardness
- 3
- Density
- 2.42 g/cm³
- Streak
- White
- Luster
- Silky
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Fibrous, Acicular, Radiating Masses
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphic Skarns
- Typical price
- $20-100 per specimen
Where rockhounds find foshagite
Classic worldwide localities
- Crestmore, California, USA
- Skellefteå, Sweden
- Khibiny Massif, Russia
- Broadford, Scotland
Field-hunting tip
Look in metamorphic skarns country — that is the host setting where foshagite typically forms. If you start seeing calcite, wollastonite, vesuvianite in float, you are in the right ground. Field specimens usually show a fibrous, acicular, radiating masses habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find foshagite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
