Ferro-gedrite is a rare iron-rich member of the orthorhombic amphibole group found in medium to high-grade metamorphic rocks. It typically appears as brownish-black, bladed or fibrous masses and can be difficult to distinguish from anthophyllite without chemical analysis.
Is this ferro-gedrite?
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 ferro-gedrite with a known reference. Ferro-gedrite sits at Mohs 5-6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ferro-gedrite leaves a grayish white streak.
- 3Read the lusterHold the specimen under a strong light. Ferro-gedrite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dark brown, brownish black, gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic to fibrous, often massive or bladed.
Often confused with
Ferro-gedrite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Ferro-gedrite leaves grayish white, Anthophyllite leaves white.
How to tell apart: Streak differs — Ferro-gedrite leaves grayish white, Hornblende leaves grayish-white.
How to tell apart: Streak differs — Ferro-gedrite leaves grayish white, Gedrite leaves white.
Often found alongside ferro-gedrite
Minerals reported to co-occur with ferro-gedrite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- □Fe₂⁺(Fe₄⁺²Al₂)Si₆Al₂O₂₂(OH)₂
- Mohs hardness
- 5-6
- Density
- 3.4-3.6 g/cm³
- Streak
- Grayish White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic to Fibrous, Often Massive or Bladed
- Cleavage
- Perfect Prismatic
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphic Rocks
- Typical price
- $10-50 per specimen depending on crystal size
Where rockhounds find ferro-gedrite
Classic worldwide localities
- Bamle, Norway
- Orijärvi, Finland
- Goshen, Massachusetts, USA
- Broken Hill, Australia
Field-hunting tip
Look in metamorphic rocks country — that is the host setting where ferro-gedrite typically forms. If you start seeing garnet, cordierite, staurolite in float, you are in the right ground. Field specimens usually show a prismatic to fibrous, often massive or bladed habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferro-gedrite?+
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How much is ferro-gedrite worth?+
What rocks look like ferro-gedrite?+
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Find ferro-gedrite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
