How to identify Andradite

To correctly identify Andradite (Andradite), 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

   Variable, including green (Demantoid), yellow (Topazolite), brown, black (Melanite), and reddish-brown. The green color of Demantoid is due to trace amounts of chromium and/or iron.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to adamantine, particularly in Demantoid, which can exhibit a diamond-like luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically granular or massive, but well-formed crystals are common.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Commonly dodecahedral (12-sided) or trapezohedral (24-sided) crystals, or a combination of both. Crystals are often euhedral to subhedral.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

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

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Contact metamorphic aureoles, skarns, serpentinites, alkaline igneous rocks, hydrothermally altered rocks. Often associated with minerals like epidote, chlorite, calcite, and magnetite.

Key Facts

Hardness

6.5-7 on the Mohs scale

Specific Gravity

3.85-3.99 g/cm³

Crystal System

Isometric

Color

Green (Demantoid), yellow (Topazolite), brown, black (Melanite), reddish-brown

Luster

Vitreous to adamantine

Transparency

Transparent to opaque

Fracture

Conchoidal to uneven

Cleavage

None

Composition

Calcium iron silicate, Ca3Fe2(SiO4)3

Physical characteristics

• Crystal Habit: Typically dodecahedral, trapezohedral, or a combination of both; also massive or granular.
• Cleavage Type: Absent
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Vitreous to adamantine

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