Cryptomelane is a manganese oxide mineral typically found as botryoidal or fibrous crusts in oxidized mineral deposits. It is often indistinguishable from other 'psilomelane' group minerals without chemical analysis, appearing as a dull to submetallic black mass.
Is this cryptomelane?
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 cryptomelane with a known reference. Cryptomelane sits at Mohs 6-6.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Cryptomelane leaves a brownish black streak.
- 3Read the lusterHold the specimen under a strong light. Cryptomelane typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: black, gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: botryoidal, massive, or fibrous crusts.
Often confused with
Cryptomelane vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Cryptomelane leaves brownish black, Romanèchite leaves shiny brownish black; luster reads submetallic on Cryptomelane and submetallic to dull on Romanèchite.
How to tell apart: Streak differs — Cryptomelane leaves brownish black, Pyrolusite leaves black; luster reads submetallic on Cryptomelane and metallic on Pyrolusite.
How to tell apart: Cryptomelane is noticeably harder (Mohs 6-6.5 vs. 4); streak differs — Cryptomelane leaves brownish black, Manganite leaves dark reddish-brown.
Often found alongside cryptomelane
Minerals reported to co-occur with cryptomelane. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K(Mn⁴⁺,Mn²⁺)₈O₁₆
- Mohs hardness
- 6-6.5
- Density
- 4.2-4.5 g/cm³
- Streak
- Brownish Black
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Botryoidal, Massive, Or Fibrous Crusts
- Cleavage
- None
- Rarity
- Common
- Uses
- Collector, Ore
- Host rock
- Oxidized Manganese Deposits
- Typical price
- $10-60 per specimen
Where rockhounds find cryptomelane
1 mapped spotsClassic worldwide localities
- Sitapar, India
- Bisbee, Arizona, USA
- Postmasburg, South Africa
- Thuringia, Germany
Field-hunting tip
Look in oxidized manganese deposits country — that is the host setting where cryptomelane typically forms. If you start seeing pyrolusite, manganite, hausmannite in float, you are in the right ground. Field specimens usually show a botryoidal, massive, or fibrous crusts habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Pennsylvania — start trip planning there.
Common questions
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Find cryptomelane on the map
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