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 1.5-2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ranciéite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Ranciéite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: black, brownish black.
- 5Look at form & habitCrystal system: trigonal. Typical habit: platy, earthy, botryoidal, or powdery aggregates.
Often confused with
Ranciéite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Romanèchite is the harder of the two (Mohs 5-6 vs. 1.5-2.5); streak differs — Ranciéite leaves brown, Romanèchite leaves shiny brownish black; luster reads submetallic on Ranciéite and submetallic to dull on Romanèchite.
How to tell apart: Pyrolusite is the harder of the two (Mohs 6-6.5 vs. 1.5-2.5); streak differs — Ranciéite leaves brown, Pyrolusite leaves black; luster reads submetallic on Ranciéite and metallic on Pyrolusite.
How to tell apart: Streak differs — Ranciéite leaves brown, Birnessite leaves brownish-black; luster reads submetallic 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
- 1.5-2.5
- Density
- 3.3-3.6 g/cm³
- Colors
- Streak
- Brown
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Platy, Earthy, Botryoidal, Or Powdery Aggregates
- Cleavage
- Perfect On {0001}
- Rarity
- Uncommon
- Uses
- Collector, Scientific Research
- Host rock
- Manganese Ore Deposits and Hydrothermal Veins
- Typical price
- $15-60 for small samples
Where rockhounds find ranciéite
Classic worldwide localities
- Rancié, France
- Sierra Nevada, USA
- Kuruman, South Africa
- Hartz Mountains, Germany
Field-hunting tip
Look in manganese ore deposits and hydrothermal veins country — that is the host setting where ranciéite typically forms. If you start seeing hausmannite, pyrolusite, calcite in float, you are in the right ground. Field specimens usually show a platy, earthy, botryoidal, or powdery aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find ranciéite on the map
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