sedimentary

Banded Agate / Jasper (Chert Pebble)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness of 6.5-7 on Mohs scale; displaying sub-vitreous to waxy luster; features distinct concentric banding and irregular veinlets with shades of reddish-brown iron oxides, white chalcedony, and dark grey-black chert/jasper matrix. Cryptocrystalline structure.

Identified July 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as a rounded river or beach pebble through secondary deposition of silica within volcanic cavities or sedimentary fracture zones, followed by erosion, transport, and natural water-smoothing.

Uses & applications

Used primarily for lapidary work, decorative carving, tumbled stones, and gemstone collecting.

Geological facts

Banded silica stones like agates and jasper get their vivid reddish and brown colors from iron mineral inclusions (such as hematite and goethite) during secondary crystallization.

Field identification & locations

Commonly found in riverbeds, streams, and coastal gravels in volcanic terrain across the Philippines (Mindanao region). Identified by its high scratch resistance (harder than steel), waxy conchoidal fracture surfaces, and distinct multi-colored banding.

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