How to identify Andradite Garnet in Skarn

To correctly identify Andradite Garnet in Skarn (Andradite (Ca3Fe2(SiO4)3) in Skarn), 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

   Andradite garnet in skarn typically exhibits colors ranging from dark green (demantoid variety), yellowish-green (topazolite variety), brown, reddish-brown, to black (melanite variety). The skarn matrix can be highly variable, often greenish, brownish, or grayish.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to resinous, sometimes adamantine (especially in demantoid).

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Skarn is typically coarse-grained, often massive or banded. Andradite crystals can be euhedral (well-formed), subhedral, or anhedral, disseminated throughout the calc-silicate matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Andradite commonly forms dodecahedral (12-sided) or trapezohedral (24-sided) crystals. These forms are characteristic of the garnet group.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Garnets are known for their lack of cleavage, exhibiting conchoidal to subconchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Contact metamorphic zones between igneous intrusions (granitoids) and carbonate sedimentary rocks (limestone, dolostone). Often found in association with ore deposits.

Key Facts

Hardness

6.5-7.5 (Mohs scale)

Specific Gravity

3.85-3.99 g/cm³

Crystal System

Isometric (Cubic)

Color

Dark green (demantoid), yellowish-green (topazolite), brown, reddish-brown, black (melanite)

Luster

Vitreous to resinous, sometimes adamantine

Transparency

Transparent to opaque

Fracture

Conchoidal to subconchoidal

Cleavage

None

Composition

Calcium iron silicate (Ca3Fe2(SiO4)3)

Physical characteristics

• Crystal Habit: Typically dodecahedral or trapezohedral crystals, also massive, granular, or compact.
• Cleavage Type: None
• Fracture Type: Conchoidal to subconchoidal
• Tenacity: Brittle
• Luster Type: Vitreous to resinous, occasionally adamantine

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