How to identify Iron Ore

To correctly identify Iron Ore (Iron Ore (likely Limonite/Goethite with 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

   Typically yellowish-brown, reddish-brown, dark brown, or black. The color can be highly variable depending on the degree of hydration and impurities. Quartz will appear colorless, white, or grey.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Earthy, dull, submetallic, or silky (for fibrous Goethite). Quartz will have a vitreous (glassy) luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Often massive, botryoidal, stalactitic, or concretionary. Can be earthy, porous, or compact. The quartz component can be granular, crystalline, or cherty.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Limonite/Goethite rarely forms distinct crystals; typically massive, reniform, botryoidal, stalactitic, or oolitic aggregates. Quartz forms hexagonal prisms with pyramidal terminations when euhedral, but is often anhedral or granular within the ore.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Limonite/Goethite lacks distinct cleavage. Quartz exhibits no cleavage but has a conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in oxidized zones of iron-bearing mineral deposits, bog iron deposits, lateritic soils, and as cementing material in sandstones and conglomerates. Also common in gossans (weathered caps of sulfide deposits).

Key Facts

Hardness

Limonite/Goethite: 4-5.5 (Mohs); Quartz: 7 (Mohs)

Specific Gravity

Limonite/Goethite: 2.7-4.3 (variable due to porosity and impurities); Quartz: 2.65

Crystal System

Limonite (amorphous/cryptocrystalline); Goethite: Orthorhombic; Quartz: Trigonal

Color

Yellowish-brown, reddish-brown, dark brown, black (Limonite/Goethite); colorless, white, grey (Quartz)

Luster

Earthy, dull, submetallic, silky (Limonite/Goethite); vitreous (Quartz)

Transparency

Opaque (Limonite/Goethite); Transparent to translucent (Quartz)

Fracture

Uneven to conchoidal (Limonite/Goethite); Conchoidal (Quartz)

Cleavage

None (Limonite/Goethite); None (Quartz)

Composition

Hydrated iron oxides (primarily FeO(OH) for Goethite) mixed with Silicon Dioxide (SiO2)

Physical characteristics

• Crystal Habit: Limonite/Goethite: Massive, botryoidal, stalactitic, reniform, oolitic, earthy. Quartz: Granular, massive, prismatic crystals (less common in ore).
• Cleavage Type: None
• Fracture Type: Uneven to conchoidal (Limonite/Goethite); Conchoidal (Quartz)
• Tenacity: Brittle
• Luster Type: Earthy, dull, submetallic, silky (Limonite/Goethite); Vitreous (Quartz)

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