How to identify Orbicular Jasper

To correctly identify Orbicular Jasper (Chalcedony (microcrystalline quartz) with various mineral 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

   Highly variable, often a mix of colors including white, cream, yellow, orange, red, brown, green, and black, arranged in concentric orbicular patterns against a contrasting matrix.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to waxy, sometimes vitreous on freshly broken surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fine-grained, dense, and compact. The surface can be smooth when polished, but rough and conchoidal on fracture surfaces.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Cryptocrystalline; individual quartz crystals are microscopic and not visible to the naked eye. The macroscopic form is massive with distinctive orbicular structures.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, due to its cryptocrystalline nature.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in areas of past volcanic activity, particularly associated with rhyolitic flows or tuffs, or in sedimentary environments where silica-rich fluids have permeated and altered existing rocks. Hydrothermal alteration zones are common settings. It can also be found in alluvial deposits as weathered nodules.

Key Facts

Hardness

6.5-7 on the Mohs scale.

Specific Gravity

2.58-2.91 g/cm³, typically around 2.65 g/cm³.

Crystal System

Trigonal (for the constituent quartz crystals, but macroscopically massive).

Color

Extremely varied, often a combination of white, cream, yellow, orange, red, brown, green, and black, arranged in orbicular patterns.

Luster

Dull, waxy, or sub-vitreous.

Transparency

Opaque.

Fracture

Conchoidal to sub-conchoidal, splintery.

Cleavage

None.

Composition

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

Physical characteristics

• Crystal Habit: Massive, cryptocrystalline, forming nodules or veins with distinctive orbicular structures.
• Cleavage Type: Absent.
• Fracture Type: Conchoidal to sub-conchoidal, splintery.
• Tenacity: Brittle.
• Luster Type: Dull, waxy, or sub-vitreous.

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