How to identify Moss Agate

To correctly identify Moss Agate (Chalcedony (a variety of Quartz) with dendritic 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

   Base color is typically colorless, white, gray, or milky white. Inclusions are green, black, brown, or reddish, forming moss-like or tree-like patterns.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to waxy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to slightly granular, cryptocrystalline.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Massive, botryoidal, mammillary, or stalactitic aggregates; individual crystals are microscopic.

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

   Occurs in amygdaloidal cavities and fissures of volcanic rocks (e.g., basalts, andesites), as well as in hydrothermal veins and as nodules in sedimentary rocks (e.g., limestones, sandstones) where silica-rich groundwater has precipitated.

Key Facts

Hardness

6.5-7 on the Mohs scale.

Specific Gravity

2.58-2.64.

Crystal System

Trigonal (cryptocrystalline aggregates).

Color

Colorless, white, gray, or milky white base with green, black, brown, or reddish dendritic inclusions.

Luster

Vitreous to waxy.

Transparency

Translucent to opaque.

Fracture

Conchoidal to uneven.

Cleavage

None.

Composition

Silicon dioxide (SiO2) with inclusions of manganese or iron oxides/hydroxides, or chlorite.

Physical characteristics

• Crystal Habit: Cryptocrystalline, typically massive, botryoidal, mammillary, or as vein fillings and nodules.
• Cleavage Type: None.
• Fracture Type: Conchoidal to uneven.
• Tenacity: Brittle.
• Luster Type: Vitreous to waxy.

Explore Moss Agate