mineral

Agate

Silicon Dioxide (SiO2) - variety of Chalcedony

Hardness: 6.5–7 on Mohs scale; Color: Multi-colored, often with translucent white, orange, or grey; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Multi-colored, often with translucent white, orange, or grey
Luster: Waxy to vitreous

Identified March 21, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary mineral in the cavities (vesicles) of igneous rocks, particularly basalt or rhyolite, as silica-rich groundwater leaches through. Agates can vary from millions to over a billion years old depending on the host rock formation.

Uses & applications

Used widely in making jewelry (cabochons), lapidary art, and industrial components like mortar and pestles due to its hardness. Also popular as a metaphysical and collector stone.

Geological facts

Ancient Greeks and Romans used agates for signet rings and decorative amulets. One unique feature of agates is their banding, caused by rhythmic crystallization of silica in rock cavities.

Field identification & locations

Identify in the field by looking for a 'waxy' texture, translucency when held to light, and irregular pits on the surface. Commonly found along beaches (like Agate Beach in WA or OR), riverbeds, and volcanic regions. Collectors look for unique inclusions or distinct 'fortification' banding.

Other mineral specimens

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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)]

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Epidote

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

mineral