How to identify Iron Ore

To correctly identify Iron Ore (Hematite / Goethite / Limonite), 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

   Hematite: Steel-gray to reddish-brown to black. Goethite/Limonite: Yellowish-brown to dark brown. Magnetite: Black.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Hematite: Metallic to dull earth. Goethite/Limonite: Dull, earthy. Magnetite: Metallic to submetallic.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Can be massive, earthy, botryoidal, reniform, micaceous (specular hematite), or oolitic.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hematite: Rhombohedral, tabular, botryoidal, massive. Goethite: Orthorhombic, often fibrous, botryoidal, stalactitic, massive. Limonite: Amorphous, massive, earthy. Magnetite: Isometric, octahedral, granular, massive.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Hematite: None, but may show parting. Goethite/Limonite: None. Magnetite: None.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Banded Iron Formations (BIFs) in ancient cratons, lateritic weathering profiles, hydrothermal veins, contact metamorphic deposits, magmatic segregations.

Key Facts

Hardness

Hematite: 5-6.5; Goethite: 5-5.5; Limonite: 4-5.5; Magnetite: 5.5-6.5 (Mohs scale)

Specific Gravity

Hematite: 4.9-5.3; Goethite: 3.3-4.3; Limonite: 2.7-4.3; Magnetite: 5.17-5.18

Crystal System

Hematite: Trigonal; Goethite: Orthorhombic; Limonite: Amorphous; Magnetite: Isometric

Color

Variable: steel-gray, reddish-brown, black, yellowish-brown

Luster

Metallic, submetallic, dull, earthy

Transparency

Opaque

Fracture

Hematite: Uneven to subconchoidal; Goethite: Uneven; Limonite: Earthy; Magnetite: Uneven to conchoidal

Cleavage

None for all primary iron ore minerals, though hematite may show parting.

Composition

Iron oxides and hydroxides (Fe2O3, FeO(OH), Fe3O4)

Physical characteristics

• Crystal Habit: Hematite: Rhombohedral, tabular, botryoidal, reniform, massive, micaceous (specular). Goethite: Prismatic, acicular, fibrous, botryoidal, stalactitic, massive. Limonite: Massive, earthy, concretionary. Magnetite: Octahedral, granular, massive.
• Cleavage Type: None (Hematite may exhibit parting on {1011})
• Fracture Type: Uneven, subconchoidal, conchoidal, earthy
• Tenacity: Brittle
• Luster Type: Metallic, submetallic, dull, earthy

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