Jasper and Basalt Mix (Dark Chert/Basalt River Pebble)

Physical Properties

Hardness: 6-7 (Mohs scale), Color: Dark grey to charcoal black with slight mottling, Luster: Waxy to dull, Crystal Structure: Microcrystalline, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.5-3.0

Formation & Geological History

Formed through either volcanic cooling (basalt) or chemical precipitation of silica (chert/jasper). This specific specimen shows signs of fluvial erosion, having been weathered and rounded in a river or stream environment over thousands of years.

Uses & Applications

Common river stones are used primarily in landscaping, decorative aquariums, and occasionally for lapidary tumbling. In ancient times, such hard stones were used as tools or grinding stones.

Geological Facts

Dark, smooth pebbles like this are often referred to as 'touchstones.' Historically, jewelers used them to test the purity of gold by observing the color of the streak left behind on the stone's surface.

Field Identification & Locations

Identify in the field by its smooth, water-worn texture, high density, and hardness (it should scratch glass). Common in riverbeds, glacial tills, and coastal beaches globally.

Identified on: 4/22/2026

Mode: Standard