How to identify Ruby in Zoisite

To correctly identify Ruby in Zoisite (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 vibrant green (zoisite), opaque red (ruby), and often black (hornblende). The green can vary from light to dark, and the red of the ruby can be purplish-red to brownish-red.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Zoisite: Vitreous to pearly. Ruby: Adamantine to vitreous. Hornblende: Vitreous to dull.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically granular to massive, with visible individual crystals of zoisite, ruby, and hornblende. The ruby crystals are often anhedral to subhedral, embedded within the zoisite matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Zoisite: Prismatic, often elongated. Ruby: Hexagonal prisms, often tabular or barrel-shaped, but typically anhedral to subhedral in this rock. Hornblende: Prismatic.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Zoisite: Perfect on {010}. Ruby: None (parting on {0001} and {1011} can occur). Hornblende: Two distinct cleavages at approximately 56 and 124 degrees.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Metamorphic terrains, particularly those associated with regional metamorphism of mafic or ultramafic rocks, often in amphibolite facies conditions, with subsequent metasomatic alteration.

Key Facts

Hardness

Zoisite: 6-7 (Mohs). Ruby: 9 (Mohs). Hornblende: 5-6 (Mohs). The overall rock hardness will vary depending on the proportions of its constituent minerals.

Specific Gravity

3.2-3.6 (variable, depending on the proportions of zoisite, ruby, and hornblende)

Crystal System

Zoisite: Orthorhombic. Ruby (Corundum): Hexagonal (Trigonal). Hornblende: Monoclinic.

Color

Green, red, black.

Luster

Vitreous to pearly.

Transparency

Opaque to translucent (zoisite), Opaque (ruby), Opaque (hornblende).

Fracture

Zoisite: Uneven to conchoidal. Ruby: Conchoidal to uneven. Hornblende: Uneven.

Cleavage

Zoisite: Perfect on {010}. Ruby: None (parting). Hornblende: Two distinct cleavages at 56 and 124 degrees.

Composition

A rock composed of calcium aluminum silicate hydroxide (zoisite), aluminum oxide (ruby/corundum), and complex calcium magnesium iron aluminum silicate hydroxide (hornblende).

Physical characteristics

• Crystal Habit: Massive to granular aggregate, with embedded prismatic zoisite and anhedral to subhedral ruby crystals.
• Cleavage Type: Zoisite: Perfect. Ruby: None (parting). Hornblende: Prismatic.
• Fracture Type: Uneven to conchoidal.
• Tenacity: Brittle.
• Luster Type: Vitreous to pearly.

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