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 — Groutite leaves brownish black, Manganite leaves dark reddish-brown.
How to tell apart: Streak differs — 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 — that is 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.
