Minnesotaite is an iron-rich phyllosilicate mineral closely related to the talc group. It is found almost exclusively in iron formations, appearing as fibrous or fine-grained plates that are typically yellow-green to brownish in color.
Is this minnesotaite?
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 minnesotaite with a known reference. Minnesotaite sits at Mohs 1.5-2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: greasy to waxy, dull.
- 4Match the color rangeCompare against the expected color range: pale green.
- 5Look at form & habitCrystal system: triclinic. Typical habit: foliated, radial.
Often confused with
Minnesotaite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside minnesotaite
Minerals reported to co-occur with minnesotaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₃Si₄O₁₀(OH)₂
- Mohs hardness
- 1.5-2
- Density
- 3.01 g/cm³
- Colors
- Streak
- White
- Luster
- Greasy to waxy, dull
- Transparency
- Semitransparent
- Crystal system
- Triclinic
- Crystal habit
- Foliated, radial
- Cleavage
- Perfect micaceous on {001}
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- In banded iron formations subjected to low-grade regional metamorphism
Where rockhounds find minnesotaite
3 mapped spotsClassic worldwide localities
- Mesabi and Cuyuna districts, St. Louis Co., Minnesota, USA
- A number of places in the Sokoman Iron Formation, Howells River area, Labrador, Newfoundland, Canada
- Blue Bell mine, Riondel, British Columbia, Canada
- Mamatwan mine, near Kuruman, Cape Province, South Africa
- Emilia-San Valentin Pb-Zn deposit, Sierra de Cartagena, Murcia Province, Spain
- Tynagh, near Killimor, Co. Galway, Ireland
Field-hunting tip
Where it forms: In banded iron formations subjected to low-grade regional metamorphism. If you start seeing quartz, siderite, stilpnomelane in float, you are in the right ground. Typical habit: foliated, radial. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Minnesota. Start trip planning there.
Common questions
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Find minnesotaite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
