How to identify Plume Agate

To correctly identify Plume Agate (Chalcedony (cryptocrystalline quartz) with inclusions), 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

   Matrix typically colorless, white, gray, or light brown; plumes can be red, orange, yellow, brown, black, white, green, or blue.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Waxy to dull on unpolished surfaces; vitreous (glassy) when polished.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to slightly granular on unpolished surfaces; conchoidal fracture surfaces are smooth.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Cryptocrystalline, meaning individual crystals are microscopic and not visible to the naked eye. Forms botryoidal, mammillary, or stalactitic masses within cavities.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Exhibits conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Primarily found in amygdaloidal cavities and veins within volcanic rocks (e.g., basalt, rhyolite, andesite) and sometimes in hydrothermal veins in other rock types. Also found as nodules in sedimentary deposits where silica-rich waters have permeated.

Key Facts

Hardness

6.5-7 on the Mohs scale (due to chalcedony matrix).

Specific Gravity

2.58-2.64 g/cm³.

Crystal System

Trigonal (for quartz/chalcedony).

Color

Translucent to opaque matrix (colorless, white, gray, brown) with colored inclusions (red, orange, yellow, brown, black, white, green, blue).

Luster

Waxy to dull (unpolished); vitreous (polished).

Transparency

Translucent to opaque.

Fracture

Conchoidal.

Cleavage

None.

Composition

Silicon dioxide (SiO₂) with various mineral inclusions (e.g., iron oxides, manganese oxides, chlorite).

Physical characteristics

• Crystal Habit: Cryptocrystalline aggregates, often botryoidal, mammillary, or stalactitic, filling cavities. Inclusions form dendritic or feathery patterns.
• Cleavage Type: None.
• Fracture Type: Conchoidal, producing smooth, curved surfaces.
• Tenacity: Brittle.
• Luster Type: Waxy to dull on rough surfaces; vitreous when polished.

Explore Plume Agate