Likely chert or weathered flint

Dark olive-brown, opaque, with a waxy-to-dull luster and irregular conchoidal-looking surfaces; apparent hardness about 6.5–7 Mohs, no obvious cleavage. The rounded triangular shape may reflect natural weathering or tumbling.

Chert forms when microcrystalline quartz replaces silica-rich sediment or accumulates as siliceous sediment, commonly in marine or chalk environments. Its exact age cannot be determined from the photograph; chert-bearing gravel may be reworked and much younger than its source rock.

Used historically for sharp tools and fire-starting; attractive pieces are collected, but this small specimen has little commercial value unless it proves to be an unusual material.

The brown-green coloration may come from iron oxides or glauconite. It could also be a dark jasper-like chert, but the image does not show diagnostic banding or translucent quartz.

The reported Louisiana location lies in unconsolidated Gulf Coastal Plain sediments, where transported chert or gravel is more plausible than an exposed local bedrock outcrop. A steel scratch test (should not scratch it), conchoidal fracture, and lack of fizz in dilute acid support chert; confirm with a fresh edge and stronger lighting.