mineral

Chalcedony (Agate/Carnelian)

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: translucent yellowish-orange to tan; Luster: waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.64.

Hardness: 6
Color: translucent yellowish-orange to tan
Luster: waxy to vitreous

Identified June 11, 2026More mineral →

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Physical properties

Formation & geological history

Formed via the deposition of silica from groundwater in cavities of volcanic and sedimentary rocks. Common in basaltic vugs.

Uses & applications

Used in jewelry, lapidary carvings, as semiprecious gemstones, and historically for artisanal tools and seals.

Geological facts

The name Chalcedony comes from the ancient Greek town Chalcedon. It has been used for beads and cylinder seals since the Bronze Age in Mesopotamia.

Field identification & locations

Identified by its waxy luster, translucency, and lack of visible crystals. Commonly found in riverbeds, beaches, and desert pavements as water-worn pebbles.

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

Biotite Schist

Biotite-rich Schist [K(Mg,Fe)3AlSi3O10(F,OH)2]

metamorphic