Howieite is a rare sodium-manganese-iron silicate typically found as dark, fibrous, or platy masses within metamorphosed sedimentary rocks. It is most famous for its occurrence in the Franciscan Complex of California, where it forms in association with other rare silicates like deerite and zussmanite. Collectors prize it for its unique chemistry and specific geological occurrence in high-pressure, low-temperature metamorphic environments.
Is this howieite?
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 howieite with a known reference. Howieite 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. Howieite leaves a brownish streak.
- 3Read the lusterHold the specimen under a strong light. Howieite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dark brown, black, dark green.
- 5Look at form & habitCrystal system: triclinic. Typical habit: fibrous, radiated, or lamellar aggregates.
Often confused with
Howieite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Deerite is the harder of the two (Mohs 6 vs. 5); streak differs — Howieite leaves brownish, Deerite leaves brown; luster reads vitreous on Howieite and submetallic on Deerite.
How to tell apart: Howieite is noticeably harder (Mohs 5 vs. 3); streak differs — Howieite leaves brownish, Zussmanite leaves white.
Often found alongside howieite
Minerals reported to co-occur with howieite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaMn²⁺₂Fe³⁺₃Si₁₂O₃₀(OH)₁₁
- Mohs hardness
- 5
- Density
- 3.38 g/cm³
- Streak
- Brownish
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Fibrous, Radiated, Or Lamellar Aggregates
- Cleavage
- Good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphic Rocks of The Franciscan Complex
- Typical price
- $20-150 per specimen
Where rockhounds find howieite
Classic worldwide localities
- Laytonville, California, USA
- Franciscan Complex, California, USA
- Cozumel, Mexico
Field-hunting tip
Look in metamorphic rocks of the franciscan complex country — that is the host setting where howieite typically forms. If you start seeing deerite, zussmanite, quartz in float, you are in the right ground. Field specimens usually show a fibrous, radiated, or lamellar aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find howieite on the map
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