How to identify Tiger Iron

To correctly identify Tiger Iron (Tiger Iron (a banded rock composed of hematite, jasper, and tiger's eye)), 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 banding of metallic dark grey/black (hematite), red/brown (jasper), and golden-brown/yellow (tiger's eye).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Varies within the rock: metallic (hematite), dull to vitreous (jasper), silky to chatoyant (tiger's eye).

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fine-grained to microcrystalline, with a fibrous appearance in the tiger's eye bands. Often exhibits a smooth, polished feel when worked.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Not applicable as a rock; individual mineral components have their own crystal forms (e.g., hematite can be massive, platy; quartz is microcrystalline).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None for the rock as a whole. Individual minerals may exhibit cleavage (e.g., hematite has no true cleavage but can show parting).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Formed within ancient banded iron formations (BIFs) that have undergone subsequent low-grade regional metamorphism and hydrothermal alteration, leading to the silicification and replacement of original minerals by quartz varieties.

Key Facts

Hardness

6.5-7 on the Mohs scale (due to quartz components), though hematite is 5-6.5.

Specific Gravity

Approximately 3.3-4.0, varying with the proportion of hematite (SG ~5.3) to quartz (SG ~2.65).

Crystal System

Not applicable as a rock; individual components are trigonal (quartz) and hexagonal/rhombohedral (hematite).

Color

Banded dark metallic grey/black, red/brown, and golden-brown/yellow.

Luster

Mixed: metallic, dull/vitreous, silky/chatoyant.

Transparency

Opaque.

Fracture

Conchoidal to uneven.

Cleavage

None (as a rock).

Composition

A composite rock primarily composed of hematite (Fe2O3), jasper (SiO2), and tiger's eye (SiO2 with fibrous inclusions).

Physical characteristics

• Crystal Habit: Massive, banded (for the rock); individual minerals are microcrystalline (jasper, tiger's eye) or massive/platy (hematite).
• Cleavage Type: None.
• Fracture Type: Conchoidal to uneven.
• Tenacity: Brittle.
• Luster Type: Mixed: metallic (hematite), dull to vitreous (jasper), silky to chatoyant (tiger's eye).

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