How to identify Lapis Lazuli

To correctly identify Lapis Lazuli (Lapis Lazuli (a metamorphic rock containing 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 streaks (calcite) and golden flecks (pyrite). The blue color is typically uniform but can show variations.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to greasy, sometimes vitreous on fractured surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fine-grained to medium-grained, massive. Can appear granular due to the intergrowth of constituent minerals.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Lapis Lazuli is a rock, so it does not have a single crystal form. Lazurite, its primary component, typically forms dodecahedral crystals, but in Lapis Lazuli, it is usually massive and anhedral (lacking well-formed crystal faces).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Lapis Lazuli, as a rock, does not exhibit cleavage. Its constituent minerals have cleavage: lazurite has imperfect cleavage on {110}, calcite has perfect rhombohedral cleavage, and pyrite has no 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 granitic intrusions or other igneous bodies that provide the necessary heat and metasomatic fluids.

Key Facts

Hardness

5 to 5.5 (Mohs scale, due to the mixture of minerals)

Specific Gravity

2.7 to 2.9 (variable depending on mineral composition)

Crystal System

Lapis Lazuli is a rock; lazurite (its primary component) is isometric (cubic).

Color

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

Luster

Dull to greasy, sometimes vitreous.

Transparency

Opaque

Fracture

Uneven to conchoidal

Cleavage

None (as a rock); lazurite has imperfect cleavage, calcite has perfect rhombohedral cleavage.

Composition

A metamorphic rock composed primarily of lazurite (Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)], calcite (CaCO3), and pyrite (FeS2). May also contain sodalite, hauyne, diopside, and other silicates.

Physical characteristics

• Crystal Habit: Massive, granular (for the rock); lazurite can form dodecahedral crystals but is usually anhedral within the rock.
• Cleavage Type: Not applicable for the rock; constituent minerals vary.
• Fracture Type: Uneven to conchoidal
• Tenacity: Brittle
• Luster Type: Dull to greasy

Explore Lapis Lazuli