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. Streak: black gray.
- 3Read the lusterHold the specimen under a strong light. Luster: submetallic.
- 4Match the color rangeCompare against the expected color range: 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, so Deerite leaves black gray, Howieite leaves grayish black; luster reads submetallic on Deerite and greasy on Howieite.
How to tell apart: Deerite is noticeably harder (Mohs 6 vs. 3); streak differs, so Deerite leaves black gray, 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
- 3.837 g/cm³
- Colors
- Streak
- Black gray
- Luster
- Submetallic
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular or fibrous crystals, often as radiating sprays or matted aggregates
- Cleavage
- Good on {110}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In meta-ironstones and Cu-Fe sulfide deposits, in blueschist facies metasediments formed at high pressure and low temperature
Where rockhounds find deerite
Classic worldwide localities
- Laytonville quarry, at Covelo, and at Burn's Flats, Mendocino Co., California, USA
- Ward Creek, Cazadero, Sonoma Co., California, USA
- Panoche Pass, San Benito Co., California, USA
- Wild Horse Lookout, Curry Co., and in the Powers quarry, Coos Co., Oregon, USA
- Salbertrand, Viafiorcia, and Beth-Ghinivert, Piedmont, Italy
- Termignon, Haute-Savoie, France
Field-hunting tip
Where it forms: In meta-ironstones and Cu-Fe sulfide deposits, in blueschist facies metasediments formed at high pressure and low temperature. If you start seeing howieite, zussmanite, stilpnomelane in float, you are in the right ground. Typical habit: acicular or fibrous crystals, often as radiating sprays or matted aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify deerite?+
Where is deerite found?+
What rocks look like deerite?+
What minerals are found with deerite?+
What kind of rock does deerite form in?+
What is deerite used for?+
Find deerite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
