How to identify Iron Ore (with Sulfides and Iron Oxides)

To correctly identify Iron Ore (with Sulfides and Iron Oxides) (Iron ore (likely containing pyrite/chalcopyrite and goethite/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

   Variable. Iron oxides typically impart red (hematite), reddish-brown to yellow-brown (goethite), or black (magnetite) colors. Sulfides, especially pyrite, are brassy yellow; chalcopyrite is brassy yellow with a greenish tinge. The overall color will be a mix.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Iron oxides can range from dull earthy (goethite, some hematite) to submetallic (hematite) to metallic (magnetite). Sulfides typically exhibit a distinct metallic luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Can be massive, banded (BIFs), granular, or disseminated. Sulfides may occur as distinct crystals, veins, or disseminated grains within the iron oxide matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Pyrite often forms cubes, octahedra, or pyritohedra. Chalcopyrite typically forms tetrahedral crystals or massive aggregates. Hematite can be platy (specularite), botryoidal, or earthy. Goethite is often fibrous, botryoidal, or earthy. Magnetite forms octahedra or dodecahedra.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Pyrite and chalcopyrite have poor to indistinct cleavage. Hematite has no true cleavage but may exhibit parting. Goethite has one perfect cleavage. Magnetite has no cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in a wide range of environments including ancient marine sedimentary basins (BIFs), hydrothermal veins, contact metamorphic zones (skarns), magmatic intrusions, and weathered profiles (laterites). The presence of both sulfides and oxides suggests environments where redox conditions fluctuated or where different mineralizing fluids interacted.

Key Facts

Hardness

Pyrite: 6-6.5; Chalcopyrite: 3.5-4; Hematite: 5-6.5; Goethite: 5-5.5; Magnetite: 5.5-6.5 (Mohs scale)

Specific Gravity

Pyrite: 4.95-5.10; Chalcopyrite: 4.1-4.3; Hematite: 5.26; Goethite: 3.3-4.3; Magnetite: 5.17-5.18

Crystal System

Pyrite: Isometric; Chalcopyrite: Tetragonal; Hematite: Trigonal; Goethite: Orthorhombic; Magnetite: Isometric

Color

As described above, highly variable depending on mineral proportions.

Luster

As described above, highly variable depending on mineral proportions.

Transparency

Opaque

Fracture

Pyrite: Uneven to conchoidal; Chalcopyrite: Conchoidal; Hematite: Uneven to subconchoidal; Goethite: Uneven; Magnetite: Uneven to conchoidal

Cleavage

Pyrite: Indistinct; Chalcopyrite: Poor; Hematite: None (parting common); Goethite: Perfect on {010}; Magnetite: None

Composition

Primarily iron (Fe) in various oxidation states and mineral forms (oxides, sulfides). May contain sulfur (S), copper (Cu), oxygen (O), and hydroxyl (OH).

Physical characteristics

• Crystal Habit: Variable: Cubic, octahedral, pyritohedral (pyrite); tetrahedral, massive (chalcopyrite); platy, botryoidal, earthy (hematite); fibrous, botryoidal, earthy (goethite); octahedral, dodecahedral, massive (magnetite).
• Cleavage Type: Variable: Indistinct to poor (sulfides), none to perfect (oxides).
• Fracture Type: Variable: Uneven, conchoidal, subconchoidal.
• Tenacity: Brittle for all listed minerals.
• Luster Type: Metallic to submetallic to earthy.

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