How to identify Galena with Iron Oxide Staining

To correctly identify Galena with Iron Oxide Staining (Galena (PbS) with 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

   The galena itself is lead-gray to silvery-gray. The iron oxide staining will appear as yellow, orange, brown, or reddish-brown coatings or patches on the galena surface. The streak of galena is lead-gray, while the streak of the iron oxides (goethite/limonite) is yellowish-brown to brownish-yellow.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Fresh galena exhibits a bright metallic luster. The iron oxide staining will typically have an earthy, dull, or sub-metallic luster, often obscuring the metallic luster of the underlying galena.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Galena typically has a massive, granular, or crystalline texture, often forming cubic or cubo-octahedral crystals. The iron oxide staining will appear as a powdery, earthy, or sometimes botryoidal coating on the galena.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Galena commonly forms cubic, cubo-octahedral, or octahedral crystals. It can also be massive or granular. The iron oxides are typically amorphous or cryptocrystalline, forming crusts or coatings.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Galena has perfect cubic cleavage in three directions at 90 degrees, producing characteristic step-like fractures or perfect cubes when broken. The iron oxide staining does not exhibit cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in hydrothermal veins, contact metamorphic deposits, and sedimentary exhalative deposits where galena has been subjected to weathering and oxidation, often in the upper parts of ore bodies (gossans) or in zones of supergene enrichment.

Key Facts

Hardness

2.5-2.75 (Galena); 5-5.5 (Goethite); 1-5.5 (Limonite, variable)

Specific Gravity

7.4-7.6 (Galena); 3.3-4.3 (Goethite/Limonite)

Crystal System

Isometric (Galena); Orthorhombic (Goethite); Amorphous/Cryptocrystalline (Limonite)

Color

Lead-gray (Galena); Yellow, orange, brown, reddish-brown (Iron Oxides)

Luster

Metallic (Galena); Earthy, dull, sub-metallic (Iron Oxides)

Transparency

Opaque (Galena and Iron Oxides)

Fracture

Subconchoidal to uneven (Galena, but typically breaks along cleavage); Uneven to splintery (Goethite/Limonite)

Cleavage

Perfect cubic in three directions at 90 degrees (Galena); None (Goethite/Limonite)

Composition

Lead sulfide (PbS) for galena; Hydrated iron oxide-hydroxide (FeO(OH)·nH2O) for goethite/limonite

Physical characteristics

• Crystal Habit: Cubic, cubo-octahedral, octahedral, massive, granular (Galena); Botryoidal, stalactitic, earthy, massive (Goethite/Limonite)
• Cleavage Type: Perfect cubic {001} (Galena)
• Fracture Type: Subconchoidal to uneven (Galena); Uneven to splintery (Goethite/Limonite)
• Tenacity: Brittle (Galena and Iron Oxides)
• Luster Type: Metallic (Galena); Earthy, dull, sub-metallic (Iron Oxides)

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