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. Ferrosaponite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Ferrosaponite typically shows a earthy luster.
- 4Match the color rangeCompare against the expected color range: green, yellowish-green, brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive.
Often confused with
Ferrosaponite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Luster reads earthy on Ferrosaponite and dull on Saponite.
How to tell apart: Luster reads earthy on Ferrosaponite and pearly on Chlorite.
How to tell apart: Streak differs — Ferrosaponite leaves white, Nontronite leaves yellow; luster reads earthy on Ferrosaponite and 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
- (Fe²⁺,Mg)₃(Si,Al)₄O₁₀(OH)₂·4H₂O
- Mohs hardness
- 2
- Density
- 2.3-2.5 g/cm³
- Streak
- White
- Luster
- Earthy
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Massive
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Veins
- Typical price
- $10-50 per specimen
Where rockhounds find ferrosaponite
Classic worldwide localities
- Germany
- Czech Republic
- Poland
Field-hunting tip
Look in hydrothermal veins country — that is the host setting where ferrosaponite typically forms. If you start seeing calcite, quartz, magnetite in float, you are in the right ground. Field specimens usually show a massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find ferrosaponite on the map
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