How to identify Lapis Lazuli and Amethyst

To correctly identify Lapis Lazuli and Amethyst (Lapis Lazuli (a rock composed primarily of lazurite, calcite, and pyrite) and Amethyst (a variety of quartz, SiO2)), 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

   Lapis Lazuli: Intense azure to violet-blue, often with white calcite veins and golden pyrite specks. Amethyst: Shades of purple, from pale lilac to deep violet, sometimes with red or blue flashes.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Lapis Lazuli: Dull to greasy. Amethyst: Vitreous (glassy).

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Lapis Lazuli: Fine-grained to granular, often with visible inclusions. Amethyst: Crystalline, typically forming prismatic crystals or drusy coatings.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Lapis Lazuli: Massive, granular. Lazurite crystals within the rock are typically dodecahedral but rarely visible. Amethyst: Hexagonal prisms terminating in rhombohedral faces, often forming geodes or druzy crusts.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Lapis Lazuli: Poor to indistinct (due to its composite nature). Lazurite itself has indistinct cleavage. Amethyst: None (conchoidal fracture).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Lapis Lazuli: Contact metamorphic zones, particularly in metamorphosed limestones or marbles. Amethyst: Hydrothermal veins, vugs, and geodes within igneous (especially basaltic) and metamorphic rocks.

Key Facts

Hardness

Lapis Lazuli: 5-5.5 (Mohs); Amethyst: 7 (Mohs)

Specific Gravity

Lapis Lazuli: 2.7-2.9; Amethyst: 2.65

Crystal System

Lapis Lazuli: Isometric (lazurite component); Amethyst: Trigonal

Color

Lapis Lazuli: Azure to violet-blue; Amethyst: Purple

Luster

Lapis Lazuli: Dull to greasy; Amethyst: Vitreous

Transparency

Lapis Lazuli: Opaque; Amethyst: Transparent to translucent

Fracture

Lapis Lazuli: Uneven to conchoidal; Amethyst: Conchoidal

Cleavage

Lapis Lazuli: Poor/Indistinct; Amethyst: None

Composition

Lapis Lazuli: Rock composed of lazurite (Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)], calcite (CaCO3), and pyrite (FeS2); Amethyst: Silicon Dioxide (SiO2)

Physical characteristics

• Crystal Habit: Lapis Lazuli: Massive, granular; Amethyst: Prismatic, often in geodes or drusy aggregates
• Cleavage Type: Lapis Lazuli: Poor to indistinct (lazurite); Amethyst: None
• Fracture Type: Lapis Lazuli: Uneven to conchoidal; Amethyst: Conchoidal
• Tenacity: Lapis Lazuli: Brittle; Amethyst: Brittle
• Luster Type: Lapis Lazuli: Dull to greasy; Amethyst: Vitreous

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