sedimentary

Jasper and Basalt (Lake Superior Agate or Jasper Pebble)

Silicified rock / Cryptocrystalline quartz (SiO2) with basalt matrix

Hardness of 6.5 to 7 on the Mohs scale, colors ranging from deep red and brown to grey and black, waxy to vitreous luster, microcrystalline (cryptocrystalline) quartz structure, conchoidal fracture with no true cleavage, specific gravity around 2.60 to 2.66.

Identified August 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the hydrothermal alteration and silicification of volcanic rocks (like basalt) where silica-rich fluids permeated the rock, replacing original minerals with microcrystalline quartz over millions of years, often dating to the Precambrian era.

Uses & applications

Used primarily in lapidary arts for tumbling, cabochons, jewelry making, and as a popular specimen for rock collectors.

Geological facts

Red jasper coloration is primarily due to iron oxide inclusions within the quartz matrix. Pebbles like this are frequently smoothed and rounded by glacial action and wave action along lake shores and rivers.

Field identification & locations

Easily identified by its smooth, water-worn exterior, high hardness that scratches glass, and opaque rich red and dark patterned appearance. Commonly found in gravel beds, glacial tills, and beaches, particularly around the Great Lakes region.

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