mineral

Chalcedony (Agate/Chert)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: White, tan, and yellowish-brown with translucent areas, Luster: Waxy to vitreous, Crystal structure: Trigonal (microcrystalline), Cleavage: None/Conchoidal fracture, Specific gravity: 2.58-2.64

Hardness: 6

Identified June 20, 2026More mineral →

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Physical properties

Formation & geological history

Formed via the deposition of silica from groundwater in cavities or veins of volcanic or sedimentary rocks. It often occurs as nodules or botryoidal masses as silica-rich fluids precipitate over time.

Uses & applications

Used frequently in lapidary work, jewelry (beads and cabochons), and as a collector's specimen. Historically used for making stone tools due to its sharp conchoidal fracture.

Geological facts

Agate and Chalcedony are often called 'earth diamonds' by rockhounds due to their durability. This specific piece shows characteristic iron staining and a smooth, water-worn texture likely from a riverbed.

Field identification & locations

Identify in the field by its waxy luster, translucency when held to a light source, and inability to be scratched by a steel knife. Common in gravel pits, riverbeds, and volcanic regions.

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral