How to identify Hawk's Eye

To correctly identify Hawk's Eye (Blue Tiger's Eye (variety of Tiger's Eye, a form of Quartz)), 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

   Dark blue-gray to blue-green, sometimes with hints of brown or black. The blue hue is distinct from the golden-brown of classic Tiger's Eye.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Silky to vitreous, especially on polished surfaces, due to the fibrous inclusions.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fine-grained, fibrous structure visible under magnification, leading to a smooth feel when polished.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically massive, cryptocrystalline aggregates, rarely showing macroscopic crystal forms of quartz. The fibrous structure is a pseudomorph after crocidolite.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, as it is a cryptocrystalline quartz. It exhibits conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in metamorphosed iron formations, particularly those rich in crocidolite. It forms in veins or layers within these host rocks.

Key Facts

Hardness

7 on the Mohs scale (due to quartz).

Specific Gravity

2.64 - 2.71 g/cm³.

Crystal System

Trigonal (for quartz), but the macroscopic form is massive fibrous.

Color

Blue-gray, blue-green, sometimes with dark streaks.

Luster

Silky to vitreous.

Transparency

Opaque.

Fracture

Conchoidal to splintery (due to fibrous structure).

Cleavage

None.

Composition

Silicon dioxide (SiO₂) with embedded, unoxidized crocidolite fibers.

Physical characteristics

• Crystal Habit: Massive, fibrous aggregates, pseudomorphous after crocidolite.
• Cleavage Type: None.
• Fracture Type: Conchoidal to splintery.
• Tenacity: Brittle.
• Luster Type: Silky to vitreous.

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