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. Streak: brownish black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic to dull.
- 4Match the color rangeCompare against the expected color range: black, gray, blue gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: botryoidal, cryptocrystalline, massive.
Often confused with
Cryptomelane vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads metallic to dull on Cryptomelane and submetallic on Psilomelane.
How to tell apart: Streak differs, so Cryptomelane leaves brownish black, Pyrolusite leaves black, bluish black.
How to tell apart: Cryptomelane is noticeably harder (Mohs 6-6.5 vs. 4); streak differs, so Cryptomelane leaves brownish black, Manganite leaves reddish brown to nearly black; luster reads metallic to dull on Cryptomelane and submetallic on Manganite.
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
- 4.17-4.41 g/cm³
- Streak
- Brownish black
- Luster
- Metallic to dull
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Botryoidal, cryptocrystalline, massive
- Cleavage
- None
- Rarity
- Common
- Uses
- Collector, Ore
- Host rock
- Widespread in oxidized manganese deposits as open-space fillings or replacing primary manganese-bearing minerals; commonly replaced by other secondary manganese minerals
Where rockhounds find cryptomelane
1 mapped spotsClassic worldwide localities
- Oregon-Prompter mine, Tombstone, Cochise Co., in the Hardshell and Mowry mines, Santa Cruz Co., and the Artillery Mountains, Mohave Co., Arizona, USA
- Lake Valley, Sierra Co., New Mexico, USA
- Silver Cliff district, Custer Co., Colorado, USA
- Philipsburg, Granite Co., Montana, USA
- Urucum, Mato Grosso, Brazil
- Oriente Province, Cuba
Field-hunting tip
Where it forms: Widespread in oxidized manganese deposits as open-space fillings or replacing primary manganese-bearing minerals; commonly replaced by other secondary manganese minerals. If you start seeing pyrolusite, nsutite, braunite in float, you are in the right ground. Typical habit: botryoidal, cryptocrystalline, massive. 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
How do you identify cryptomelane?+
Where is cryptomelane found?+
Can I find cryptomelane in the United States?+
What rocks look like cryptomelane?+
What minerals are found with cryptomelane?+
What kind of rock does cryptomelane form in?+
What is cryptomelane used for?+
Find cryptomelane on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
