sedimentary

Iron-rich chert or jasper

Microcrystalline quartz (SiO₂), variably stained by iron oxides/hydroxides

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque mustard-yellow to brown with gray translucent edges, earthy to dull luster, and no visible cleavage. The layered, waxy-looking fracture and rusty coloration are consistent with iron-stained chert/jasper, though exact identification requires testing.

Identified August 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when silica precipitated or replaced sediment, later acquiring yellow-brown limonite/goethite staining; commonly Precambrian to younger. It occurs in bedded sedimentary formations, weathered iron-rich zones, and hydrothermal environments.

Uses & applications

Used as rough or polished ornamental stone, cabochons, beads, and lapidary material; massive low-grade pieces have little industrial value compared with silica-rich aggregate.

Geological facts

Chert is composed of microscopic quartz crystals and commonly breaks with a curved, conchoidal fracture. Yellow coloration usually reflects limonite or goethite rather than the quartz itself.

Field identification & locations

Check for a glassy/conchoidal fracture, inability to scratch it with a steel knife, and a white streak; a strong magnetic response would instead suggest magnetite-rich ironstone. Common in iron-formations and silicified sedimentary outcrops worldwide.