mineral

Agate

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5–7; Color: Creamy white to translucent with a reddish-brown matrix; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Specific gravity: 2.58–2.64

Hardness: 6
Color: Creamy white to translucent with a reddish-brown matrix
Luster: Waxy to vitreous

Identified June 13, 2026More mineral →

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Physical properties

Hardness: 6.5–7; Color: Creamy white to translucent with a reddish-brown matrix; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Specific gravity: 2.58–2.64

Formation & geological history

Formed as secondary deposits in cavities (vesicles) within igneous volcanic rocks, such as basalt. Silica-rich groundwater permeates these pockets, depositing layers of chalcedony over thousands to millions of years.

Uses & applications

Used primarily in lapidary arts for jewelry, bead making, and ornamental carvings. Historically used for making mortars and pestles due to its hardness.

Geological facts

The specimen shown appears to be a whole or split agate nodule, often called a 'Thunder Egg' depending on its locality. Agates are named after the Achates River in Sicily where they were first discovered.

Field identification & locations

Identify in the field by looking for a waxy luster on broken surfaces, a translucent quality when held to light, and an often rough, bumpy exterior 'skin' that hides the interior crystal or band structure. Common in the Pacific Northwest and volcanic regions.