Ferrosilite is an iron-rich member of the orthopyroxene group, typically found in high-grade metamorphic rocks and sometimes igneous rocks. It is noted for its dark, often brownish-black color and is chemically the iron end-member of the enstatite-ferrosilite series. Collectors should look for its characteristic cleavage and associated iron-rich mineral suites in metamorphic complexes.
Is this ferrosilite?
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 ferrosilite with a known reference. Ferrosilite 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. Ferrosilite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Ferrosilite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: brown, dark brown, black, gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals, massive, granular.
Often confused with
Ferrosilite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Ferrosilite leaves white, Hypersthene leaves greyish-white; luster reads vitreous on Ferrosilite and submetallic on Hypersthene.
How to tell apart: Streak differs — Ferrosilite leaves white, Augite leaves grayish white.
Often found alongside ferrosilite
Minerals reported to co-occur with ferrosilite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₂Si₂O₆
- Mohs hardness
- 5-6
- Density
- 3.9-4.0 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic Crystals, Massive, Granular
- Cleavage
- Good in 2 Directions
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Metamorphic Iron Formations and Charnockites
- Typical price
- $20-150 thumbnail to small cabinet
Where rockhounds find ferrosilite
Classic worldwide localities
- Hitra, Norway
- Mount Hay, Australia
- Adirondack Mountains, USA
- Greenland
Field-hunting tip
Look in metamorphic iron formations and charnockites country — that is the host setting where ferrosilite typically forms. If you start seeing magnetite, quartz, fayalite in float, you are in the right ground. Field specimens usually show a prismatic crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find ferrosilite on the map
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