Ferrosaponite is a rare iron-rich member of the saponite group, typically found as earthy, massive coatings or fillings in hydrothermal environments. It is characterized by its dull green to brownish hue and soft, clay-like consistency, often requiring XRD analysis for positive identification.
Is this ferrosaponite?
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 ferrosaponite with a known reference. Ferrosaponite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: dark green, brownish green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: columnar, radial, spherical.
Often confused with
Ferrosaponite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Ferrosaponite leaves green, Saponite leaves white; luster reads vitreous on Ferrosaponite and greasy on Saponite.
How to tell apart: Streak differs, so Ferrosaponite leaves green, Chlorite leaves white; luster reads vitreous on Ferrosaponite and pearly on Chlorite.
How to tell apart: Streak differs, so Ferrosaponite leaves green, Nontronite leaves white; luster reads vitreous on Ferrosaponite and waxy, resinous, dull on Nontronite.
Often found alongside ferrosaponite
Minerals reported to co-occur with ferrosaponite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₀.₃(Fe,Mg,Fe)₃(Si,Al)₄O₁₀(OH)₂·4H₂O
- Mohs hardness
- 2
- Density
- 2.49 g/cm³
- Colors
- Streak
- Green
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Columnar, radial, spherical
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A hydrothermal mineral associated with pillow basalts
Where rockhounds find ferrosaponite
Classic worldwide localities
- Levoberezhye “Iceland spar” deposit, near the Nizhnyaya Tunguska River, Evenkiya, Siberia, Russia
Field-hunting tip
Where it forms: A hydrothermal mineral associated with pillow basalts. If you start seeing calcite, pyrite, quartz in float, you are in the right ground. Typical habit: columnar, radial, spherical. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferrosaponite?+
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What rocks look like ferrosaponite?+
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Find ferrosaponite on the map
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