How to identify Lapis Lazuli

To correctly identify Lapis Lazuli (Lapis Lazuli (a metamorphic rock containing lazurite, pyrite, and calcite)), 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 golden flecks (pyrite) and white streaks or patches (calcite). The blue color is typically uniform but can vary in intensity.

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, granular, massive. Can feel slightly rough due to the presence of different minerals.

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. The constituent mineral lazurite typically forms dodecahedral crystals, but these are rarely visible in the massive rock. Pyrite may appear as small, disseminated euhedral to anhedral grains.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Lapis Lazuli, as a rock, does not exhibit cleavage. Its constituent mineral lazurite has imperfect dodecahedral cleavage, but this is not typically observed in the rock mass. Calcite has perfect rhombohedral 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, where metasomatic alteration has occurred due to the intrusion of igneous bodies (e.g., granites). These environments provide the necessary chemical components (sulfur, sodium, aluminum, silicon) and thermal conditions for lazurite formation.

Key Facts

Hardness

5 to 6 (Mohs scale)

Specific Gravity

2.7 to 2.9

Crystal System

Isometric (for lazurite, the primary blue mineral component)

Color

Intense azure blue to violet-blue

Luster

Dull 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)], with calcite (CaCO3), pyrite (FeS2), and often sodalite, hauyne, and diopside.

Physical characteristics

• Crystal Habit: Massive, granular (for the rock); dodecahedral (for individual lazurite crystals, rarely visible)
• Cleavage Type: None (as a rock); imperfect dodecahedral (for lazurite)
• Fracture Type: Uneven to conchoidal
• Tenacity: Brittle
• Luster Type: Dull to greasy

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