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 3.5-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: dark brown.
- 3Read the lusterHold the specimen under a strong light. Luster: brilliant submetallic to adamantine.
- 4Match the color rangeCompare against the expected color range: blue black.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular, prismatic, striated.
Often confused with
Groutite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Groutite leaves dark brown, Manganite leaves reddish brown to nearly black; luster reads brilliant submetallic to adamantine on Groutite and submetallic on Manganite.
How to tell apart: Goethite is the harder of the two (Mohs 5-5.5 vs. 3.5-4); streak differs, so Groutite leaves dark brown, Goethite leaves brownish yellow, yellow-orange, ocher-yellow; luster reads brilliant submetallic to adamantine on Groutite and imperfect adamantine metallic to dull earthy; silky when fibrous on Goethite.
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
- 3.5-4
- Density
- 4.144 g/cm³
- Colors
- Streak
- Dark brown
- Luster
- Brilliant submetallic to adamantine
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular, prismatic, striated
- Cleavage
- {010}, perfect; {100}, less perfect
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- A secondary mineral lining vugs in weathered banded iron formations (Minnesota, USA); manganiferous talc schists (Talcville, New York, USA); a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA)
Where rockhounds find groutite
Classic worldwide localities
- Franklin, Sussex Co., New Jersey, USA
- No. Two and One Half mine, Talcville, New York, USA
- Campbell mine, Bisbee, Cochise Co., Arizona, USA
- Magma mine, Superior, and at Malpais Hill, Pinal Co., Arizona, USA
- Walton mine, Hants Co., Nova Scotia, Canada
- Bülten-Adenstadt, near Peine, Lower Saxony, Germany
Field-hunting tip
Where it forms: A secondary mineral lining vugs in weathered banded iron formations (Minnesota, USA); manganiferous talc schists (Talcville, New York, USA); a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA). If you start seeing manganite, hematite, goethite in float, you are in the right ground. Typical habit: acicular, prismatic, striated. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify groutite?+
Where is groutite found?+
What rocks look like groutite?+
What minerals are found with groutite?+
What kind of rock does groutite form in?+
What is groutite used for?+
Find groutite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
