Groutite is a rare manganese oxide mineral that typically occurs as slender, needle-like black crystals. It is frequently confused with manganite but is distinguished by its specific crystal structure and associations in manganese-rich deposits.
Is this groutite?
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 groutite with a known reference. Groutite sits at Mohs 5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Groutite leaves a brownish black streak.
- 3Read the lusterHold the specimen under a strong light. Groutite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: black, dark brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular or prismatic crystals, often in radiating clusters.
Often confused with
Groutite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Groutite is noticeably harder (Mohs 5.5 vs. 4); streak differs, so Groutite leaves brownish black, Manganite leaves dark reddish-brown.
How to tell apart: Streak differs, so Groutite leaves brownish black, Iron Ore leaves reddish-brown to black; luster reads submetallic on Groutite and metallic to submetallic on Iron Ore.
Often found alongside groutite
Minerals reported to co-occur with groutite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MnO(OH)
- Mohs hardness
- 5.5
- Density
- 4.15 g/cm³
- Colors
- Streak
- Brownish Black
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular or Prismatic Crystals, Often in Radiating Clusters
- Cleavage
- Perfect On {110}
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Sedimentary Manganese Deposits, Hydrothermal Veins
- Typical price
- $20-150 depending on specimen size and clarity
Where rockhounds find groutite
Classic worldwide localities
- Germany
- United States
- Czech Republic
- South Africa
Field-hunting tip
Look in sedimentary manganese deposits, hydrothermal veins country, the host setting where groutite typically forms. If you start seeing pyrolusite, manganite, psilomelane in float, you are in the right ground. Field specimens usually show a acicular or prismatic crystals, often in radiating clusters habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find groutite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
