How to identify Fuchsite with Black Tourmaline

To correctly identify Fuchsite with Black Tourmaline (Fuchsite (a variety of Muscovite) with Schorl (black Tourmaline)), 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 emerald green (fuchsite) with contrasting black (schorl). The green can range from pale to intense, often with a silvery sheen from the mica.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to pearly (fuchsite), vitreous to resinous (schorl). The overall rock often has a shimmering, micaceous luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Foliated or schistose due to the alignment of mica flakes (fuchsite). Schorl crystals can be prismatic, acicular, or massive, often embedded within the mica matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Fuchsite typically occurs as small, platy, hexagonal crystals or aggregates, forming a micaceous mass. Schorl forms prismatic, often striated, trigonal crystals, which can be euhedral to anhedral.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Fuchsite exhibits perfect basal cleavage (001), allowing it to split into thin, flexible sheets. Schorl has indistinct cleavage, but often exhibits conchoidal to uneven fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in medium-grade metamorphic rocks such as schists and gneisses, particularly those derived from chromium-rich protoliths (e.g., ultramafic rocks) that have undergone regional metamorphism and often metasomatism.

Key Facts

Hardness

Fuchsite: 2.5-3 on Mohs scale; Schorl: 7-7.5 on Mohs scale. The overall rock will have variable hardness.

Specific Gravity

Fuchsite: 2.77-2.88; Schorl: 3.03-3.25. The rock's specific gravity will be an average of its components.

Crystal System

Fuchsite: Monoclinic; Schorl: Trigonal

Color

Green (fuchsite), Black (schorl)

Luster

Pearly to vitreous (fuchsite), Vitreous to resinous (schorl)

Transparency

Translucent to opaque (fuchsite), Opaque (schorl)

Fracture

Uneven to splintery (fuchsite), Conchoidal to uneven (schorl)

Cleavage

Perfect basal cleavage (fuchsite), Indistinct (schorl)

Composition

Fuchsite: K(Al,Cr)2(AlSi3O10)(OH)2; Schorl: Na(Fe2+3)Al6(BO3)3Si6O18(OH)4

Physical characteristics

• Crystal Habit: Fuchsite: Micaceous, platy, foliated; Schorl: Prismatic, acicular, columnar, massive
• Cleavage Type: Fuchsite: Perfect basal (001); Schorl: Indistinct
• Fracture Type: Fuchsite: Uneven to splintery; Schorl: Conchoidal to uneven
• Tenacity: Fuchsite: Flexible, elastic; Schorl: Brittle
• Luster Type: Pearly to vitreous (fuchsite), Vitreous to resinous (schorl)

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