Ranciéite is a manganese oxide mineral typically found as earthy or botryoidal crusts within oxidized manganese deposits. It is often distinguished from other manganese minerals by its distinct brown streak and tendency to occur in fine-grained aggregates. It is most frequently encountered by collectors in samples from historic manganese mining districts.
Is this ranciéite?
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 ranciéite with a known reference. Ranciéite sits at Mohs 2.5-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale reddish brown with a lilac to purple hue.
- 3Read the lusterHold the specimen under a strong light. Luster: bright metallic.
- 4Match the color rangeCompare against the expected color range: black, violet brown, silver gray.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: lamellar, radial, stalactitic.
Often confused with
Ranciéite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Psilomelane is the harder of the two (Mohs 5-6 vs. 2.5-3); streak differs, so Ranciéite leaves pale reddish brown with a lilac to purple hue, Psilomelane leaves brownish black; luster reads bright metallic on Ranciéite and submetallic on Psilomelane.
How to tell apart: Streak differs, so Ranciéite leaves pale reddish brown with a lilac to purple hue, Pyrolusite leaves black, bluish black; luster reads bright metallic on Ranciéite and metallic on Pyrolusite.
How to tell apart: Ranciéite is noticeably harder (Mohs 2.5-3 vs. 1.5); streak differs, so Ranciéite leaves pale reddish brown with a lilac to purple hue, Birnessite leaves brownish-black; luster reads bright metallic on Ranciéite and dull on Birnessite.
Often found alongside ranciéite
Minerals reported to co-occur with ranciéite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ca,Mn²⁺)Mn⁴⁺₄O₉·3H₂O
- Mohs hardness
- 2.5-3
- Density
- 3.336 g/cm³
- Colors
- Streak
- Pale reddish brown with a lilac to purple hue
- Luster
- Bright metallic
- Transparency
- Opaque, transparent in thin fragments
- Crystal system
- Hexagonal
- Crystal habit
- Lamellar, radial, stalactitic
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- A product of weathering or alteration of manganese deposits, commonly formed in limestone or in caves in limestone
Where rockhounds find ranciéite
Classic worldwide localities
- Batesville, Independence Co., Arkansas, USA
- Mammoth Cave, Kentucky, USA
- Anson Betts mine, Plainfield, Hampshire Co., Massachusetts, USA
- Paxton’s Cave, near Bolling Springs, Alleghany Co., Virginia, USA
- Rancié, near Vicdessos, Ariège, France
- Prader, Pyrénées-Oriental, France
Field-hunting tip
Where it forms: A product of weathering or alteration of manganese deposits, commonly formed in limestone or in caves in limestone. If you start seeing todorokite, calcite, limonite in float, you are in the right ground. Typical habit: lamellar, radial, stalactitic. Train your eye for that shape before scanning the outcrop.
Common questions
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Find ranciéite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
