Deerite is a rare chain silicate mineral primarily found in high-pressure metamorphic rocks of the Franciscan Complex in California. It typically occurs as black, needle-like acicular crystals forming radiating sprays or dense fibrous mats embedded in quartz-rich matrices.
Is this deerite?
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 deerite with a known reference. Deerite 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. Deerite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Deerite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: black, brownish black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular or fibrous crystals, often as radiating sprays or matted aggregates.
Often confused with
Deerite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Deerite is noticeably harder (Mohs 6 vs. 5); streak differs — Deerite leaves brown, Howieite leaves brownish; luster reads submetallic on Deerite and vitreous on Howieite.
How to tell apart: Deerite is noticeably harder (Mohs 6 vs. 3); streak differs — Deerite leaves brown, Zussmanite leaves white; luster reads submetallic on Deerite and vitreous on Zussmanite.
Often found alongside deerite
Minerals reported to co-occur with deerite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe²⁺₆Fe³⁺₃O₃[Si₆O₁₇](OH)₅
- Mohs hardness
- 6
- Density
- 3.8-3.9 g/cm³
- Colors
- Streak
- Brown
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Acicular or Fibrous Crystals, Often as Radiating Sprays or Matted Aggregates
- Cleavage
- Perfect On {110}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metachert and High-pressure Metamorphic Glaucophane-bearing Schists
- Typical price
- $20-150 per specimen
Where rockhounds find deerite
Classic worldwide localities
- Laytonville, California, USA
- Franciscan Complex, California, USA
Field-hunting tip
Look in metachert and high-pressure metamorphic glaucophane-bearing schists country — that is the host setting where deerite typically forms. If you start seeing howieite, zussmanite, quartz in float, you are in the right ground. Field specimens usually show a acicular or fibrous crystals, often as radiating sprays or matted aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find deerite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
