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, so Ferrosilite leaves white, Hypersthene leaves greyish-white; luster reads vitreous on Ferrosilite and submetallic on Hypersthene.
How to tell apart: Streak differs, so 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, 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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