How to identify Lapis Lazuli

To correctly identify Lapis Lazuli (Lapis Lazuli (a metamorphic rock composed primarily of lazurite, calcite, and pyrite)), 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

   Intense azure blue to violet-blue, often with white calcite veins and golden pyrite flecks. The blue color is uniform in higher quality specimens.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to greasy, sometimes dull on rough surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fine-grained to medium-grained, granular, often with visible inclusions of calcite and pyrite.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Lapis Lazuli is a rock, not a single mineral, so it does not have a distinct crystal form. Lazurite, its primary component, forms dodecahedral or cubic crystals, but these are rarely visible within the rock matrix.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   No distinct cleavage as a rock. Lazurite itself exhibits imperfect dodecahedral cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in contact metamorphic zones, particularly in metamorphosed limestones or marbles, often associated with skarn deposits. It forms where sulfur-rich fluids interact with carbonate rocks at elevated temperatures and pressures.

Key Facts

Hardness

5-6 (Mohs scale)

Specific Gravity

2.7-2.9 g/cm

Crystal System

Cubic (for lazurite component, but Lapis Lazuli is a rock)

Color

Intense azure blue to violet-blue

Luster

Vitreous to greasy

Transparency

Opaque

Fracture

Uneven to conchoidal

Cleavage

None (as a rock); imperfect dodecahedral (for lazurite)

Composition

A rock composed primarily of lazurite (Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)], calcite (CaCO3), and pyrite (FeS2), with minor amounts of sodalite, hauyne, and other silicates.

Physical characteristics

• Crystal Habit: Massive, granular (as a rock); lazurite can form dodecahedral crystals but rarely visible.
• Cleavage Type: None (as a rock); imperfect dodecahedral (for lazurite).
• Fracture Type: Uneven to conchoidal.
• Tenacity: Brittle.
• Luster Type: Vitreous to greasy.

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