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 5.5-6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: grayish white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: gray, brown.
- 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, so Ferro-gedrite leaves grayish white, Anthophyllite leaves white or grayish.
How to tell apart: Streak differs, so Ferro-gedrite leaves grayish white, Hornblende leaves grayish-white.
How to tell apart: Streak differs, so Ferro-gedrite leaves grayish white, Gedrite leaves gray 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(Fe₃Al₂)(Si₆Al₂)O₂₂(OH)₂
- Mohs hardness
- 5.5-6
- Density
- 3.566 g/cm³
- Streak
- Grayish white
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic to fibrous, often massive or bladed
- Cleavage
- Perfect on {210}, intersecting at 54° and 126°
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In contact metamorphosed pelitic rocks
Where rockhounds find ferro-gedrite
Classic worldwide localities
- Mt. Yakushi, Miyamori district, Kitakami Mountainland, Iwate Prefecture, and in the Kawai mine, Ena, Gifu Prefecture, Japan
- Fisken½sset, Greenland
- Turbeoshov, Shuyeverskoya, Karelia
- Spitzenberg, Harz Mountains, Germany
Field-hunting tip
Where it forms: In contact metamorphosed pelitic rocks. If you start seeing chamosite, chlorite, andalusite in float, you are in the right ground. Typical habit: prismatic to fibrous, often massive or bladed. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferro-gedrite?+
Where is ferro-gedrite found?+
What rocks look like ferro-gedrite?+
What minerals are found with ferro-gedrite?+
What kind of rock does ferro-gedrite form in?+
What is ferro-gedrite used for?+
Find ferro-gedrite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
