Piemontite is a manganese-rich member of the epidote group, easily distinguished by its distinctive reddish-brown to cherry-red color. It typically forms in low-grade metamorphic rocks and is highly prized by collectors for its rare, well-terminated prismatic crystals or vibrant massive chunks found in alpine-type veins.
Is this piemontite?
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 piemontite with a known reference. Piemontite sits at Mohs 6-6.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: reddish.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: red, yellow, carmine red, reddish brown, reddish black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: blocky, massive, prismatic.
Often confused with
Piemontite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Piemontite leaves reddish, Epidote leaves grayish white.
How to tell apart: Streak differs, so Piemontite leaves reddish, Allanite leaves gray; luster reads vitreous on Piemontite and submetallic on Allanite.
How to tell apart: Streak differs, so Piemontite leaves reddish, Clinozoisite leaves grayish white.
Often found alongside piemontite
Minerals reported to co-occur with piemontite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂Mn³⁺Al₂(Si₂O₇)(SiO₄)O(OH)
- Mohs hardness
- 6-6.5
- Density
- 3.46-3.54 g/cm³
- Streak
- Reddish
- Luster
- Vitreous
- Transparency
- Translucent to nearly opaque
- Crystal system
- Monoclinic
- Crystal habit
- Blocky, massive, prismatic
- Cleavage
- {001}, perfect; {100}, poor
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- In regionally metamorphosed rocks of the greenschist to amphibolite facies; in metasomatized manganese deposits; in low-temperature hydrothermal veins in altered rhyolites, andesites, and diorites
Where rockhounds find piemontite
Classic worldwide localities
- Garnet Lake and in the Agnew Meadow mine, Madera Co., and in the Braito mine, Plumas Co., California, USA
- Tucson Mountains, Pima Co., Arizona, USA
- Idarado mine, Ouray Co., Colorado, USA
- Yuba Canyon, Peavine Mountain, Washoe Co., Nevada, USA
- Praborna mine, south of St. Marcel, Val d'Aosta, Piedmont, Italy
- Sörhårås and Rakten, Ultevis, Norrbotten, and at Jakobsberg and Långban, Värmland, Sweden
Field-hunting tip
Where it forms: In regionally metamorphosed rocks of the greenschist to amphibolite facies; in metasomatized manganese deposits; in low-temperature hydrothermal veins in altered rhyolites, andesites, and diorites. If you start seeing epidote, tremolite, glaucophane in float, you are in the right ground. Typical habit: blocky, massive, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify piemontite?+
Where is piemontite found?+
What rocks look like piemontite?+
What minerals are found with piemontite?+
What kind of rock does piemontite form in?+
What is piemontite used for?+
Find piemontite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
