How to identify Lapis Lazuli

To correctly identify Lapis Lazuli (Lapis Lazuli (a 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 to violet-blue, often with white calcite veins and golden pyrite specks. The blue color is due to the lazurite component.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to greasy, sometimes vitreous on freshly broken surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fine-grained to medium-grained, often granular. Can appear massive.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically massive, compact, or granular. Individual lazurite crystals are rare and usually dodecahedral.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Lazurite exhibits imperfect dodecahedral cleavage, but in the rock, it is generally not observed due to its massive nature. Calcite has perfect rhombohedral cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Formed in contact metamorphic zones, specifically in metamorphosed limestones or marbles that have been metasomatically altered by silica-poor, sulfur-rich fluids from nearby igneous intrusions.

Key Facts

Hardness

5-5.5 (Mohs scale)

Specific Gravity

2.7-2.9 g/cm³

Crystal System

Cubic (for lazurite component)

Color

Intense azure to violet-blue, often with white calcite and golden pyrite inclusions

Luster

Dull to greasy, sometimes vitreous

Transparency

Opaque

Fracture

Uneven to conchoidal

Cleavage

Imperfect dodecahedral (for lazurite), perfect rhombohedral (for calcite)

Composition

A rock composed primarily of lazurite (Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)], calcite (CaCO3), and pyrite (FeS2). Minor constituents can include sodalite, hauyne, diopside, and mica.

Physical characteristics

• Crystal Habit: Massive, granular, compact. Rarely forms distinct dodecahedral crystals.
• Cleavage Type: Imperfect dodecahedral for lazurite; perfect rhombohedral for calcite.
• Fracture Type: Uneven to conchoidal.
• Tenacity: Brittle.
• Luster Type: Dull to greasy, sometimes vitreous.

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