Jasper (Banded Argillite/Chert mix)

Physical Properties

Hardness: 6.5-7 on Mohs scale. Color: Greenish-grey with earthy brown and tan bands. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.9.

Formation & Geological History

Formed through the accumulation of fine-grained silica or clay-rich sediments that undergo diagenesis. The banding is often caused by rhythmic deposition or variations in oxygen levels and iron content during mineral replacement, typically in ancient seabed environments.

Uses & Applications

Used primarily in lapidary work for cabochons and tumbled stones, decorative landscaping, and as an ornamental material for collectors.

Geological Facts

Jasper is a variety of chalcedony that contains up to 20% foreign materials, which accounts for its wide variety of colors and patterns. This specimen appears water-worn, likely collected from a riverbed or coastal area.

Field Identification & Locations

Identify in the field by its hardness (it will scratch glass), smooth waxy feel when wet, and lack of visible grains. Look for it in glacial till or riverbeds where harder stones concentrate.

Identified on: 4/21/2026

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