carnelian

Carnelian, also known as cornelian, is a reddish-orange variety of chalcedony, a microcrystalline form of silica. The color ranges from pale orange to brick red and is typically translucent to translucent. The hue is caused by iron oxide impurities within the crystal structure.

As a chalcedony, carnelian is related to agate and jasper but is usually uniform in color rather than banded. Geologically, it forms when silica-rich solutions fill cavities in volcanic rocks and precipitate microcrystalline quartz. It commonly occurs as nodules or lenses and is often associated with other chalcedonies such as agate and jasper.

Hardness is about 6.5–7 on the Mohs scale, and the density is around 2.58–2.64 g/cm3. Natural carnelian ranges in color, but many stones sold as carnelian are heat-treated or dyed to produce a deeper red-orange color.

Major historical and commercial sources include India and Brazil, with other notable deposits in Madagascar, Uruguay, Russia, and the United States (notably Arizona). In antiquity, carnelian was valued for jewelry and engraved gems such as scarabs; it was used for signet rings and seals in ancient Egypt and Mesopotamia and remained popular in jewelry and ornamentation through the Middle Ages and into modern times.

Care and treatment: Carnelian is relatively hard and durable but should be protected from sharp blows and prolonged exposure to heat or harsh chemicals. Some dyed or heat-treated stones may require gentle handling to preserve color.