mineral

Tumbled Agate (Carnelian/Sard)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Reddish-brown, cream, and dark translucent patches; Luster: Waxy to vitreous; Crystal Structure: Hexagonal (trigonal) microcrystalline silica; Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Reddish-brown, cream, and dark translucent patches
Luster: Waxy to vitreous

Identified July 14, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a primary mineral in cavities of volcanic rocks (lavas) or in sedimentary rocks. It forms by the deposition of silica from groundwater into nodules. Most are millions of years old.

Uses & applications

Used primarily in jewelry, lapidary arts, decorative items, and as healing stones in metaphysical practices. Industrially used for mortar and pestles due to its hardness.

Geological facts

Agate is a variety of chalcedony. The reddish hues in this specimen are likely caused by iron oxide impurities. Tumbled stones like this one are smoothed in a rotary machine for weeks to achieve a polished finish.

Field identification & locations

Identify by its waxy luster, translucency when held to light, and lack of visible crystalline grains. Commonly found in riverbeds or volcanic regions globally, such as Brazil, India, and the USA.

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