How to identify Dendritic Quartz

To correctly identify Dendritic Quartz (SiO2 with 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

   Host quartz is typically colorless, white, gray, or milky. Dendrites are black, dark gray, or brownish-black.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) for the quartz; dull to sub-metallic for the manganese dendrites.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to slightly rough depending on the quartz habit and presence of surface dendrites. The dendrites themselves are typically flat, two-dimensional patterns within the quartz.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz can be massive, granular, or euhedral crystals. The dendrites exhibit a distinctive branching, fern-like, or tree-like pattern, often appearing as flat inclusions within fractures or planes.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz lacks cleavage; it exhibits conchoidal fracture. The manganese oxides do not exhibit macroscopic cleavage within the dendritic forms.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in various geological settings where quartz forms and manganese-rich fluids are present, including hydrothermal veins, sedimentary rocks (e.g., chert, limestone), and weathered zones of manganese-rich deposits. Often found in fractures, fissures, or along bedding planes within the host rock.

Key Facts

Hardness

7 on the Mohs scale for quartz; manganese oxides typically range from 2 to 6, but are inclusions within the harder quartz.

Specific Gravity

2.65 g/cm³ for quartz; manganese oxides vary (e.g., Pyrolusite ~4.4-5.0, Psilomelane ~3.7-4.7), but the overall specific gravity is dominated by quartz.

Crystal System

Trigonal for quartz; manganese oxides can be orthorhombic, monoclinic, or amorphous.

Color

Colorless, white, gray, or milky quartz with black to dark brown dendritic patterns.

Luster

Vitreous for quartz; dull to sub-metallic for dendrites.

Transparency

Transparent to translucent for quartz; opaque for dendrites.

Fracture

Conchoidal for quartz; manganese oxides are typically too fine-grained to observe distinct fracture.

Cleavage

None for quartz; manganese oxides typically lack distinct cleavage in dendritic forms.

Composition

Silicon dioxide (SiO2) with inclusions of various manganese oxides (e.g., MnO2, Mn2O3, Mn3O4).

Physical characteristics

• Crystal Habit: Quartz can be prismatic, massive, or granular. Dendrites form arborescent (tree-like) or fern-like patterns, typically two-dimensional within the host.
• Cleavage Type: Absent (quartz).
• Fracture Type: Conchoidal (quartz).
• Tenacity: Brittle (quartz).
• Luster Type: Vitreous (quartz), dull to sub-metallic (manganese oxides).

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