Ferro-ferri-hornblende is a member of the complex amphibole group, typically appearing as dark, elongated prismatic crystals. It is primarily found in metamorphic environments and certain igneous intrusions, identified by its distinct cleavage angles. Collectors typically identify this mineral through X-ray diffraction or electron microprobe analysis due to its similarity to other hornblende species.
Is this ferro-ferri-hornblende?
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-ferri-hornblende with a known reference. Ferro-ferri-hornblende 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-ferri-hornblende leaves a white to light gray streak.
- 3Read the lusterHold the specimen under a strong light. Ferro-ferri-hornblende typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: black, dark green, dark brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals, fibrous, columnar, or massive.
Often confused with
Ferro-ferri-hornblende vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Ferro-ferri-hornblende leaves white to light gray, Hornblende leaves grayish-white.
How to tell apart: Streak differs — Ferro-ferri-hornblende leaves white to light gray, Actinolite leaves white; luster reads vitreous on Ferro-ferri-hornblende and vitreous to silky on Actinolite.
How to tell apart: Streak differs — Ferro-ferri-hornblende leaves white to light gray, Arfvedsonite leaves grey to bluish-grey.
Often found alongside ferro-ferri-hornblende
Minerals reported to co-occur with ferro-ferri-hornblende. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂Fe²⁺₄Fe³⁺(Si₇Al)O₂₂(OH)₂
- Mohs hardness
- 5-6
- Density
- 3.2-3.4 g/cm³
- Streak
- White to Light Gray
- Luster
- Vitreous
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic Crystals, Fibrous, Columnar, Or Massive
- Cleavage
- Perfect in Two Directions At 56 and 124 Degrees
- Rarity
- Uncommon
- Uses
- Collector, Scientific Research
- Host rock
- Metamorphic Rocks, Igneous Rocks
- Typical price
- $10-50 per specimen
Where rockhounds find ferro-ferri-hornblende
Classic worldwide localities
- Sweden
- Norway
- Finland
- USA
Field-hunting tip
Look in metamorphic rocks, igneous rocks country — that is the host setting where ferro-ferri-hornblende typically forms. If you start seeing quartz, feldspar, biotite in float, you are in the right ground. Field specimens usually show a prismatic crystals, fibrous, columnar, or massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find ferro-ferri-hornblende on the map
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