How to identify Fuchsite

To correctly identify Fuchsite (Chromian Muscovite), 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

   Vibrant green, ranging from pale to emerald green, due to chromium content.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to pearly on cleavage surfaces, often appearing silky in massive aggregates.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically flaky, scaly, or micaceous. Can be massive or disseminated as small flakes within a host rock.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Usually occurs as anhedral to subhedral flakes or scales. Euhedral crystals are rare but would be pseudohexagonal plates.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect basal cleavage (001), allowing it to be split into thin, flexible, and elastic sheets.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Metamorphic rocks, particularly greenschist facies, associated with chromium-rich protoliths such as ultramafic rocks (e.g., serpentinites, peridotites) or chromite-bearing sediments. Often found in quartzites, schists, and marbles.

Key Facts

Hardness

2.5 - 3 on the Mohs scale

Specific Gravity

2.77 - 2.88 g/cm³

Crystal System

Monoclinic

Color

Emerald green, pale green, apple green

Luster

Vitreous to pearly on cleavage surfaces

Transparency

Transparent to translucent

Fracture

Uneven to splintery (rarely observed due to perfect cleavage)

Cleavage

Perfect basal cleavage {001}

Composition

Hydrous potassium aluminum silicate with significant chromium substitution for aluminum.

Physical characteristics

• Crystal Habit: Micaceous, flaky, scaly, massive, disseminated aggregates. Rarely in distinct pseudohexagonal crystals.
• Cleavage Type: Perfect basal cleavage on {001}, yielding thin, flexible, and elastic sheets.
• Fracture Type: Uneven to splintery, but rarely observed due to dominant cleavage.
• Tenacity: Flexible and elastic (sheets bend and return to original shape).
• Luster Type: Pearly on cleavage surfaces, vitreous on other surfaces, sometimes silky in massive forms.

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