mineral
Polished agate/jasper pebble
Microcrystalline quartz (chalcedony), SiO₂, with iron-oxide staining
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; translucent tan, orange, cream, and brown coloration with waxy to vitreous luster. The polished surface shows fine fibrous/microcrystalline quartz and possible subtle banding; cleavage is absent and fracture is conchoidal.
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Physical properties
Hardness about 6.5–7 Mohs; translucent tan, orange, cream, and brown coloration with waxy to vitreous luster. The polished surface shows fine fibrous/microcrystalline quartz and possible subtle banding; cleavage is absent and fracture is conchoidal.
Formation & geological history
Formed when silica-rich groundwater repeatedly filled cavities in volcanic rock, depositing chalcedony and quartz; orange-brown areas likely contain hematite or goethite. Such agates commonly formed in Cenozoic to older volcanic environments, though this specimen’s exact age is indeterminate.
Uses & applications
Used for cabochons, beads, carvings, tumbled stones, and decorative objects; durable slabs are also used for bookends and ornamental pieces.
Geological facts
Agate and jasper are varieties of chalcedony, and natural specimens often combine translucent chalcedony with opaque iron-rich zones. Polishing enhances the color and internal pattern.
Field identification & locations
Identify by its waxy luster, high hardness, conchoidal fracture, lack of cleavage, and translucent microcrystalline texture; a steel blade should not scratch it readily. Common sources include Brazil, Uruguay, Madagascar, India, Mexico, and the western United States.
