mineral

Carnelian Agate

Silicon Dioxide (SiO2) with iron oxide impurities

Hardness: 6.5-7 (Mohs scale), Color: Translucent orange to reddish-brown, Luster: Vitreous to waxy, Crystal Structure: Trigonal (microcrystalline/cryptocrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.58–2.64

Hardness: 6

Identified March 30, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in the cavities of igneous rocks such as basalt or rhyolite. The distinct orange hue is caused by iron oxide (hematite) impurities during formation, often dating back to the Cenozoic or Mesozoic eras.

Uses & applications

Primarily used in jewelry (beads, cabochons), lapidary arts, and ornamental carvings. Historically used for seals and signet rings because hot wax does not stick to it.

Geological facts

Ancient Romans and Greeks used carnelian for signet rings and amulets. It is one of the oldest semi-precious stones recorded in history, dating back to at least the 4th millennium BC in the Indus Valley.

Field identification & locations

Identify in the field by its waxy luster, translucency (glows when held to sun), and lack of visible crystals. It is commonly found in riverbeds or gravel deposits in areas with volcanic history, such as Brazil, India, and the Pacific Northwest (USA) - often referred to as 'Cornelian' in older texts.

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