mineral
Tumbled brown quartz/chert pebble
Microcrystalline quartz (SiO₂), possibly chert or jasper
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; translucent brown to gray-brown, with a dull to waxy luster and no visible cleavage. The rounded shape suggests natural water wear or tumbling; exact identification is limited by the photograph.
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Physical properties
Hardness about 6.5–7 Mohs; translucent brown to gray-brown, with a dull to waxy luster and no visible cleavage. The rounded shape suggests natural water wear or tumbling; exact identification is limited by the photograph.
Formation & geological history
Chert forms when silica-rich groundwater replaces or precipitates within sediment, commonly during the Mesozoic or younger sedimentary cycles; jasper is an iron-rich opaque variety. It commonly occurs as resistant pebbles in river gravels and sedimentary formations.
Uses & applications
Used for toolmaking, aggregate, decorative stone, cabochons, and inexpensive lapidary pieces. This small unpolished specimen has little commercial value.
Geological facts
Quartz-rich chert can produce a conchoidal fracture and sharp edges when broken. Brown coloration may result from iron oxides or organic impurities.
Field identification & locations
Identify with a steel-file scratch test: quartz-rich material should resist scratching, while a glassy streak or conchoidal fracture supports chert. Common sources include river gravels and limestone or chalk regions.
