How to identify Ruby in Zoisite

To correctly identify Ruby in Zoisite (Corundum (Ruby) in Zoisite), 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

   Distinctive combination of opaque green (zoisite), opaque pink to red (ruby), and black (amphibole).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Zoisite: Vitreous to pearly; Ruby: Adamantine to vitreous; Amphibole: Vitreous to dull.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Granular to massive, often with visible individual crystals of ruby and amphibole within the zoisite matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Ruby: Hexagonal prisms, often anhedral to subhedral within the matrix. Zoisite: Prismatic, often massive. Amphibole: Prismatic to acicular.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Zoisite: Perfect on {010}. Ruby: No true cleavage, but parting on {0001} and {1011}. Amphibole: Two perfect cleavages at approximately 56 and 124 degrees.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Metasomatic zones associated with the intrusion of felsic magmas into chromium-rich mafic or ultramafic rocks, under conditions of regional or contact metamorphism.

Key Facts

Hardness

Ruby: 9 (Mohs); Zoisite: 6-6.5 (Mohs); Amphibole: 5-6 (Mohs)

Specific Gravity

Ruby: 3.95-4.10; Zoisite: 3.15-3.37; Amphibole (Pargasite): 3.0-3.5

Crystal System

Ruby: Trigonal; Zoisite: Orthorhombic; Amphibole: Monoclinic

Color

Green, red, black

Luster

Vitreous to pearly, adamantine

Transparency

Opaque to translucent (individual minerals can be transparent in thin section)

Fracture

Ruby: Uneven to conchoidal; Zoisite: Uneven; Amphibole: Uneven to subconchoidal

Cleavage

Ruby: No true cleavage, parting on {0001} and {1011}; Zoisite: Perfect on {010}; Amphibole: Perfect on {110} at 56 and 124 degrees

Composition

Mixture of Corundum (Al2O3), Zoisite (Ca2Al3(SiO4)3(OH)), and Amphibole (e.g., Pargasite: NaCa2(Mg,Fe)4Al(Al2Si6O22)(OH)2)

Physical characteristics

• Crystal Habit: Ruby: Tabular, prismatic, granular; Zoisite: Prismatic, massive; Amphibole: Prismatic, acicular, massive
• Cleavage Type: Ruby: Parting; Zoisite: Perfect; Amphibole: Perfect
• Fracture Type: Uneven to conchoidal
• Tenacity: Brittle
• Luster Type: Vitreous to pearly, adamantine

Explore Ruby in Zoisite