Ferrokësterite is a rare member of the stannite group that occurs primarily as small, opaque black grains within tin-bearing ore deposits. It is chemically similar to kësterite but with iron substituting for zinc in the crystal structure, often making identification difficult without specialized chemical analysis like EDS.
Is this ferrokësterite?
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 ferrokësterite with a known reference. Ferrokësterite sits at Mohs ~4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: steel gray, gray.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: massive.
Often confused with
Ferrokësterite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Ferrokësterite leaves black, Stannite leaves blackish.
How to tell apart: Streak differs, so Ferrokësterite leaves black, Sphalerite leaves pale brown to pale yellow and white; luster reads metallic on Ferrokësterite and resinous to adamantine on Sphalerite.
Often found alongside ferrokësterite
Minerals reported to co-occur with ferrokësterite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₂FeSnS₄
- Mohs hardness
- ~4
- Density
- 4.490 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Tetragonal
- Crystal habit
- Massive
- Cleavage
- Distinct on {110}; a parting on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In greisen-bordered sulfide veins in granite
Where rockhounds find ferrokësterite
Classic worldwide localities
- Cligga mine, Perranzabuloe, Cornwall, England (type locality)
Field-hunting tip
Where it forms: In greisen-bordered sulfide veins in granite. If you start seeing arsenopyrite, cassiterite, chalcopyrite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferrokësterite?+
Where is ferrokësterite found?+
Is ferrokësterite safe to handle?+
What rocks look like ferrokësterite?+
What minerals are found with ferrokësterite?+
What kind of rock does ferrokësterite form in?+
What is ferrokësterite used for?+
Find ferrokësterite on the map
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