How to identify Orbicular Jasper

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

   Extremely variable, including reds, browns, greens, yellows, whites, greys, blacks, often multi-colored within a single specimen. The orbs themselves can be different colors from the matrix.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to vitreous (glassy) on fractured surfaces, typically dull to waxy on unpolished surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fine-grained, dense, and compact. The defining characteristic is the presence of distinct spherical or eye-like patterns (orbs) embedded within the matrix. These orbs can be smooth, concentric, or radial.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Cryptocrystalline (microcrystalline), meaning individual crystals are too small to be seen without high magnification. Forms massive aggregates.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Jasper is cryptocrystalline quartz and does not exhibit cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in a variety of geological settings, including volcanic flows (especially rhyolites), hydrothermal veins, sedimentary chert deposits, and as secondary infillings in fractures. Often associated with areas of past or present volcanic activity or silica-rich fluid circulation.

Key Facts

Hardness

6.5 - 7 on the Mohs scale

Specific Gravity

2.58 - 2.91 (average around 2.65 - 2.70)

Crystal System

Trigonal (as microcrystalline quartz)

Color

Extremely varied, often multi-colored with distinct orbicular patterns.

Luster

Dull to waxy, sometimes vitreous on fresh breaks.

Transparency

Opaque

Fracture

Conchoidal to splintery

Cleavage

None

Composition

Silicon dioxide (SiO2) with various mineral impurities (e.g., iron oxides, manganese oxides, clay minerals, chlorite) that give it color and pattern.

Physical characteristics

• Crystal Habit: Massive, cryptocrystalline aggregates, forming nodules, veins, or beds with distinctive orbicular textures.
• Cleavage Type: None
• Fracture Type: Conchoidal to splintery, typical of cryptocrystalline quartz.
• Tenacity: Brittle
• Luster Type: Dull to waxy, sometimes vitreous on fresh breaks.

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