How to identify Malachite and Limonite

To correctly identify Malachite and Limonite (Cu2(CO3)(OH)2 (Malachite) and FeO(OH)·nH2O (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

   Malachite: Bright green to dark green, often with concentric banding. Limonite: Yellowish-brown, reddish-brown, dark brown, or blackish-brown.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Malachite: Silky (fibrous varieties), vitreous to adamantine (crystalline varieties), dull (massive varieties). Limonite: Earthy, dull, sometimes submetallic.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Malachite: Often botryoidal, stalactitic, mammillary, or massive; fibrous aggregates are common. Limonite: Earthy, porous, concretionary, massive, or oolitic.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Malachite: Monoclinic system; typically forms radiating fibrous aggregates, botryoidal masses, or crusts. Rarely forms distinct prismatic crystals. Limonite: Amorphous or cryptocrystalline; does not form distinct crystals, but can form pseudomorphs after other minerals.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Malachite: Perfect on {201}, good on {001}. Limonite: None (amorphous/cryptocrystalline).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Both are secondary minerals found in the oxidized zones of ore deposits. Malachite is specifically associated with copper deposits, often in limestone or dolomite. Limonite is ubiquitous in weathered iron-rich rocks, gossans (iron hats) over sulfide deposits, and sedimentary environments like bogs and swamps.

Key Facts

Hardness

Malachite: 3.5-4 on Mohs scale; Limonite: 4-5.5 (variable due to mixture)

Specific Gravity

Malachite: 3.6-4.0; Limonite: 2.7-4.3 (variable)

Crystal System

Malachite: Monoclinic; Limonite: Amorphous/Cryptocrystalline (Goethite and Lepidocrocite are Orthorhombic)

Color

Malachite: Green; Limonite: Yellowish-brown to dark brown

Luster

Malachite: Silky, vitreous, dull; Limonite: Earthy, dull

Transparency

Malachite: Translucent to opaque; Limonite: Opaque

Fracture

Malachite: Uneven to subconchoidal; Limonite: Uneven, earthy

Cleavage

Malachite: Perfect on {201}, good on {001}; Limonite: None

Composition

Malachite: Copper carbonate hydroxide (Cu2(CO3)(OH)2); Limonite: Hydrated iron oxyhydroxides (FeO(OH)·nH2O)

Physical characteristics

• Crystal Habit: Malachite: Botryoidal, mammillary, stalactitic, fibrous, massive, rarely prismatic crystals. Limonite: Massive, earthy, concretionary, oolitic, stalactitic, pseudomorphs.
• Cleavage Type: Malachite: Perfect {201}, good {001}; Limonite: None.
• Fracture Type: Malachite: Uneven to subconchoidal; Limonite: Uneven, earthy.
• Tenacity: Malachite: Brittle; Limonite: Brittle to friable.
• Luster Type: Malachite: Silky, vitreous, dull; Limonite: Earthy, dull, sometimes submetallic.

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