Ferro-tschermakite is an iron-rich member of the amphibole supergroup, commonly found in metamorphic environments like amphibolites and schists. It typically appears as dark, prismatic, or acicular crystals that can be challenging to distinguish from other dark hornblende-group members without chemical analysis.
Is this ferro-tschermakite?
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-tschermakite with a known reference. Ferro-tschermakite 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. Streak: dark green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: dark green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals.
Often confused with
Ferro-tschermakite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Ferro-tschermakite leaves dark green, Hornblende leaves grayish-white.
How to tell apart: Streak differs, so Ferro-tschermakite leaves dark green, Tschermakite leaves greenish white.
How to tell apart: Streak differs, so Ferro-tschermakite leaves dark green, Actinolite leaves white.
Often found alongside ferro-tschermakite
Minerals reported to co-occur with ferro-tschermakite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- □Ca₂(Fe²⁺₃Al₂)(Si₆Al₂)O₂₂(OH)₂
- Mohs hardness
- 5-6
- Density
- 3.260 g/cm³
- Colors
- Streak
- Dark green
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic crystals
- Cleavage
- Perfect on {110}, with intersections at ~56° and ~124°; partings on {100} and {001}
- Rarity
- Uncommon
- Uses
- Collector, Petrological research
- Host rock
- A rock-forming mineral in granitic pegmatite in a batholith
Where rockhounds find ferro-tschermakite
Classic worldwide localities
- Granite quarries, Ploumanac’h Granitic Complex, La Clarté, Perros-Guirec, Brittany, France
- Confirmed from Ovala, Gabon, Canada
- Waits River, Vermont and Joyceville, Massachusetts, USA, Canada
- Lake Kutemajärvi and Permiö, Finland, Canada
- Frood Mine, Sudbury, Canada
Field-hunting tip
Where it forms: A rock-forming mineral in granitic pegmatite in a batholith. If you start seeing plagioclase, staurolite, almandine in float, you are in the right ground. Typical habit: prismatic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferro-tschermakite?+
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Find ferro-tschermakite on the map
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