mineral

Chalcedony (Common Opal or Agate variant)

Silicon Dioxide (SiO₂)

Hardness: 6.5-7 on Mohs scale; Color: Pinkish-purple, lavender, or bluish-grey with translucent waxy luster; Crystal structure: Microcrystalline/cryptocrystalline (trigonal); Cleavage: None; Fracture: Conchoidal (shell-like curves).

Hardness: 6

Identified March 29, 2026More mineral →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed by the precipitation of silica from groundwater in cavities of igneous rocks or sedimentary layers. Often associated with volcanic environments where hydrothermal fluids cool over thousands of years.

Uses & applications

Used primarily in lapidary arts for cabochons, carvings, and beads. Also valued as a metaphysical stone and by mineral collectors for its smooth texture and color palette.

Geological facts

Chalcedony was highly prized in the ancient world, particularly by the Greeks and Romans for seals and signet rings because hot wax does not stick to it. This specific specimen shows the characteristic waxy 'skin' of raw chalcedony nodules.

Field identification & locations

Identify in the field by its smooth, waxy surface and the absence of visible crystals. It is much harder than glass (it will scratch glass). Commonly found in the Western United States (Oregon, Arizona), Brazil, and Madagascar.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

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

Epidote

Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)

mineral