How to identify Iron Ore

To correctly identify Iron Ore (Iron Ore (likely containing goethite, limonite, or hematite)), 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

   Varies widely depending on the dominant mineral: Hematite (reddish-brown to steel-gray), Magnetite (black), Goethite/Limonite (yellowish-brown to dark brown), Siderite (pale yellow to brownish-gray).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Hematite (metallic to dull earth), Magnetite (metallic to submetallic), Goethite/Limonite (dull, earthy), Siderite (vitreous to pearly).

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Can be massive, earthy, oolitic, botryoidal, or crystalline. Often granular in BIFs.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hematite: tabular, micaceous (specularite), reniform, botryoidal, massive. Magnetite: octahedral, granular, massive. Goethite: acicular, fibrous, botryoidal, massive. Limonite: amorphous, earthy, massive. Siderite: rhombohedral, massive.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Hematite: none. Magnetite: none. Goethite: good in one direction (010). Limonite: none. Siderite: perfect rhombohedral.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in ancient marine sedimentary basins (BIFs), weathered profiles (laterites), hydrothermal veins, magmatic intrusions, and bog environments.

Key Facts

Hardness

Hematite: 5-6.5; Magnetite: 5.5-6.5; Goethite: 5-5.5; Limonite: 4-5.5; Siderite: 3.5-4.5 (Mohs scale)

Specific Gravity

Hematite: 5.26; Magnetite: 5.18; Goethite: 3.3-4.3; Limonite: 2.7-4.3; Siderite: 3.96

Crystal System

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

Color

Reddish-brown, black, steel-gray, yellow-brown, dark brown, pale yellow to brownish-gray

Luster

Metallic, submetallic, dull, earthy, vitreous, pearly

Transparency

Opaque (most iron oxides), translucent (thin splinters of goethite, siderite)

Fracture

Hematite: uneven to subconchoidal; Magnetite: subconchoidal to uneven; Goethite: uneven; Limonite: earthy; Siderite: uneven to conchoidal

Cleavage

Hematite: none; Magnetite: none; Goethite: good on {010}; Limonite: none; Siderite: perfect rhombohedral on {1011}

Composition

Iron oxides (Fe2O3, Fe3O4, FeO(OH)), iron carbonate (FeCO3), often with silica (SiO2) and other impurities.

Physical characteristics

• Crystal Habit: Massive, earthy, granular, oolitic, botryoidal, reniform, tabular, octahedral, rhombohedral, acicular, fibrous.
• Cleavage Type: Absent (hematite, magnetite, limonite), good (goethite), perfect rhombohedral (siderite).
• Fracture Type: Uneven, subconchoidal, conchoidal, earthy.
• Tenacity: Brittle (most forms), sectile (some earthy hematite).
• Luster Type: Metallic, submetallic, dull, earthy, vitreous, pearly.

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