Tumbled brown chert (likely flint)

Hardness about 6.5–7 Mohs; opaque brown to black, waxy-to-dull luster, very fine-grained with no visible crystals or cleavage. The rounded, glossy surface indicates tumbling and polishing.

Chert forms when silica replaces or accumulates within marine or freshwater sediment, commonly from biogenic silica. It occurs in sedimentary rocks ranging from Paleozoic to Cenozoic age; the specimen’s exact age cannot be determined visually.

Used historically for sharp tools and fire-starting, and today as a lapidary, craft, and decorative stone. Common tumbled pieces have modest collector value.

Its conchoidal fracture produces curved, sharp edges, a diagnostic feature of chert. Brown coloration may come from iron oxides or organic impurities.

Identify it by its glassy/waxy appearance, very high hardness, lack of cleavage, and ability to scratch ordinary glass; it typically does not fizz in dilute hydrochloric acid. Common sources include limestone and chalk regions worldwide, including England, Texas, Missouri, and the Great Lakes region.