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, so 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, 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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