How to identify Azurite-Malachite in matrix

To correctly identify Azurite-Malachite in matrix (Azurite (Cu3(CO3)2(OH)2) and Malachite (Cu2CO3(OH)2) in a host rock), 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

   Vibrant blue (azurite) and green (malachite) intergrown within a host rock. The blue can range from light sky blue to deep indigo, and the green from light apple green to dark emerald green.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Azurite: Vitreous to dull. Malachite: Silky (fibrous varieties) to dull or earthy (massive varieties). The matrix luster will vary depending on the host rock.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Can be crystalline, botryoidal, massive, or banded. Azurite often forms prismatic crystals or radiating aggregates. Malachite frequently forms botryoidal, stalactitic, or banded masses. The texture of the matrix will be characteristic of the host rock.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Azurite: Monoclinic, typically as tabular to prismatic crystals, often in radiating or granular aggregates. Malachite: Monoclinic, typically as botryoidal, stalactitic, fibrous, or massive aggregates; individual crystals are rare and acicular. The matrix will show the crystal forms of its constituent minerals.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Azurite: Good on {011}, distinct on {100}. Malachite: Perfect on {201}, good on {010}. The matrix will exhibit cleavage planes of its constituent minerals, if any.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Oxidized zones of copper ore deposits, often associated with limestone or other carbonate-rich host rocks. Found in gossans and supergene enrichment zones.

Key Facts

Hardness

Azurite: 3.5-4 on the Mohs scale. Malachite: 3.5-4 on the Mohs scale. The matrix hardness will vary.

Specific Gravity

Azurite: 3.77-3.89. Malachite: 3.90-4.03. The overall specific gravity of the matrix specimen will depend on the proportions of minerals.

Crystal System

Monoclinic for both azurite and malachite.

Color

Azurite: Azure blue, deep blue, violet-blue. Malachite: Bright green, dark green, banded green.

Luster

Azurite: Vitreous to dull. Malachite: Silky (fibrous) to dull/earthy (massive).

Transparency

Azurite: Transparent to translucent. Malachite: Translucent to opaque.

Fracture

Azurite: Conchoidal. Malachite: Uneven to sub-conchoidal.

Cleavage

Azurite: Good on {011}, distinct on {100}. Malachite: Perfect on {201}, good on {010}.

Composition

Azurite: Copper carbonate hydroxide (Cu3(CO3)2(OH)2). Malachite: Copper carbonate hydroxide (Cu2CO3(OH)2). The matrix composition varies depending on the host rock.

Physical characteristics

• Crystal Habit: Azurite: Tabular, prismatic, radiating, granular, massive. Malachite: Botryoidal, stalactitic, fibrous, massive, banded.
• Cleavage Type: Azurite: Prismatic. Malachite: Perfect basal.
• Fracture Type: Azurite: Conchoidal. Malachite: Uneven to sub-conchoidal.
• Tenacity: Brittle for both azurite and malachite.
• Luster Type: Azurite: Vitreous to dull. Malachite: Silky to dull/earthy.

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