How to identify Picture Jasper

To correctly identify Picture Jasper (Chalcedony (microcrystalline quartz) with iron oxides and other minerals), 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

   Earthy tones, predominantly browns, tans, creams, reds, and blacks, often in contrasting layers or dendritic patterns.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to waxy, sometimes sub-vitreous on freshly broken surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth, fine-grained, and dense. Opaque.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Massive, cryptocrystalline (microcrystalline aggregates). Individual crystals are not visible to the naked eye.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Exhibits a conchoidal to sub-conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in a variety of geological settings, including volcanic flows, hydrothermal veins, and sedimentary deposits. It often forms in areas where silica-rich waters percolate through existing rocks, depositing chalcedony and incorporating mineral impurities.

Key Facts

Hardness

6.5 - 7 on the Mohs scale

Specific Gravity

2.58 - 2.91

Crystal System

Trigonal (cryptocrystalline aggregates)

Color

Brown, tan, cream, red, black, often in variegated patterns.

Luster

Dull to waxy, sometimes sub-vitreous.

Transparency

Opaque.

Fracture

Conchoidal to sub-conchoidal.

Cleavage

None.

Composition

SiO2 (silicon dioxide) with various iron oxides (Fe2O3, FeO(OH)·nH2O), manganese oxides, and clay minerals as impurities.

Physical characteristics

• Crystal Habit: Massive, cryptocrystalline aggregates; individual crystals are microscopic.
• Cleavage Type: None.
• Fracture Type: Conchoidal to sub-conchoidal, splintery.
• Tenacity: Brittle.
• Luster Type: Dull to waxy, sometimes sub-vitreous.

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