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, so 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, so 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, so 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, 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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