How to identify Amethyst Geode

To correctly identify Amethyst Geode (Amethyst (variety of Quartz)), 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

   The defining characteristic is the purple to violet color of the internal quartz crystals. The outer shell is typically dull grey, brown, or reddish.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) on the crystal faces of the amethyst. The outer rock shell may be dull to earthy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   The outer surface is typically rough or nodular. The inner surface is crystalline, feeling sharp or granular due to the individual crystal terminations.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hexagonal prisms terminated by rhombohedral faces, often forming a druse (a layer of small, closely packed crystals) lining the geode cavity.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Quartz exhibits conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found within volcanic rocks (e.g., basalt flows, tuffs) or sedimentary rocks (e.g., limestones, shales) where cavities have formed and subsequently been filled by hydrothermal silica solutions.

Key Facts

Hardness

7 on the Mohs scale (for the quartz crystals).

Specific Gravity

2.65 g/cm³ (for the quartz crystals).

Crystal System

Trigonal (for the quartz crystals).

Color

Purple to violet (amethyst crystals); outer shell varies.

Luster

Vitreous (glassy) on crystal faces; outer shell can be dull to earthy.

Transparency

Transparent to translucent (amethyst crystals); opaque (outer shell).

Fracture

Conchoidal (for the quartz crystals).

Cleavage

None.

Composition

Silicon dioxide (SiO₂) with trace iron impurities (Fe3+) responsible for the color.

Physical characteristics

• Crystal Habit: Prismatic hexagonal crystals, often terminated by rhombohedral faces, forming a druse lining a cavity.
• Cleavage Type: Absent.
• Fracture Type: Conchoidal.
• Tenacity: Brittle.
• Luster Type: Vitreous.

Explore Amethyst Geode