Tumbled agate/chalcedony pebble

Hardness about 6.5–7 Mohs; brown, reddish, and translucent gray zones; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage; specific gravity about 2.6.

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing layered chalcedony and quartz over long periods, commonly during the Cenozoic or older volcanic episodes. Its smooth shape indicates natural stream/beach abrasion or tumbling.

Used as a decorative pebble, cabochon, bead, and lapidary material; attractive pieces may be polished for jewelry or collecting.

Agate is a variety of chalcedony distinguished by translucency and banding, while jasper is more opaque and impurity-rich; this specimen appears partly translucent but lacks enough detail for a precise variety identification.

Common in volcanic terrains and gravel beaches, especially Oregon, Washington, California, Brazil, Uruguay, India, and Madagascar. Field tests include scratching glass, resisting steel scratching, and showing translucency at thin edges; avoid confusing it with slag or colored glass.