How to identify Manganese Dendrites

To correctly identify Manganese Dendrites (Manganese oxides), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Typically black to dark brown, sometimes with a bluish or purplish tint.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to sub-metallic, often earthy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth on the host rock surface, but the dendritic patterns are often slightly raised or etched into the surface.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Dendritic (tree-like, fern-like, branching) aggregates; individual crystals are microscopic and anhedral.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Not applicable to the dendritic aggregate; individual manganese oxide minerals may have cleavage but it's not observable in dendrites.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Commonly found in sedimentary rocks (limestone, sandstone, shale), especially along bedding planes, fractures, and within geodes or concretions. Also found in weathered igneous and metamorphic rocks.

Key Facts

Hardness

Varies depending on the specific manganese oxide mineral, generally 2 to 6 on the Mohs scale (e.g., pyrolusite ~2-2.5, cryptomelane ~6). The aggregate itself is often soft and easily scratched.

Specific Gravity

Varies, typically 3.7 to 5.0, depending on the specific manganese oxide minerals present.

Crystal System

Variable (monoclinic, tetragonal, orthorhombic, amorphous) depending on the specific manganese oxide mineral(s) forming the dendrite.

Color

Black, dark brown, sometimes with a bluish or purplish tint.

Luster

Dull, earthy, sub-metallic.

Transparency

Opaque.

Fracture

Not applicable to the aggregate; individual minerals may show uneven to conchoidal fracture.

Cleavage

Not applicable to the aggregate; individual minerals may have cleavage (e.g., pyrolusite has perfect cleavage).

Composition

Hydrous manganese oxides (MnO2, MnO(OH), etc.) with varying amounts of other metal ions (e.g., Ba, K, Na, Fe) and water.

Physical characteristics

• Crystal Habit: Dendritic (arborescent, fern-like, branching aggregates). Individual crystals are microcrystalline to cryptocrystalline.
• Cleavage Type: Not observable in dendrites; individual minerals vary.
• Fracture Type: Not observable in dendrites; individual minerals vary (uneven to conchoidal).
• Tenacity: Brittle to friable, depending on the specific mineral and degree of cementation.
• Luster Type: Dull, earthy, sub-metallic.

Explore Manganese Dendrites