Tephroite is a manganese-rich member of the olivine group typically found in metamorphosed manganese deposits. Collectors often look for its characteristic flesh-red or brownish-gray granular masses, which are frequently associated with fluorescent minerals like willemite at localities such as Franklin, New Jersey.
Is this tephroite?
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 tephroite with a known reference. Tephroite sits at Mohs 6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale gray.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to greasy.
- 4Match the color rangeCompare against the expected color range: reddish brown, gray, olive green, bluish green, red.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: granular, massive, prismatic.
Often confused with
Tephroite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Forsterite is the harder of the two (Mohs 7 vs. 6); streak differs, so Tephroite leaves pale gray, Forsterite leaves white.
How to tell apart: Streak differs, so Tephroite leaves pale gray, Fayalite leaves white.
How to tell apart: Streak differs, so Tephroite leaves pale gray, Rhodonite leaves white.
Often found alongside tephroite
Minerals reported to co-occur with tephroite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn₂SiO₄
- Mohs hardness
- 6
- Density
- 3.87-4.12 g/cm³
- Streak
- Pale gray
- Luster
- Vitreous to greasy
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Granular, massive, prismatic
- Cleavage
- {010}, distinct; {001}, imperfect
- Rarity
- Uncommon
- Uses
- Collector, Research
- Host rock
- In Fe{Mn ore deposits, related skarns, and metamorphosed manganese-rich sediments
Where rockhounds find tephroite
2 mapped spotsClassic worldwide localities
- Franklin and Sterling Hill, Ogdensburg, Sussex Co., New Jersey, USA
- Bald Knob, near Sparta, Alleghany Co., North Carolina, USA
- Sunnyside mine, San Juan Co., Colorado, USA
- Buritirama, Piaui, Brazil
- Harstigen mine, near Persberg, Sweden
- Långban, Värmland, Sweden
Field-hunting tip
Where it forms: In Fe{Mn ore deposits, related skarns, and metamorphosed manganese-rich sediments. If you start seeing zincite, willemite, franklinite in float, you are in the right ground. Typical habit: granular, massive, prismatic. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in California, New Jersey. Start trip planning there.
Common questions
How do you identify tephroite?+
Where is tephroite found?+
Can I find tephroite in the United States?+
What rocks look like tephroite?+
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Find tephroite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
