Carnelian

Carnelian is a variety of chalcedony - microcrystalline quartz composed of tiny interlocking crystals invisible to the naked eye. It forms when silica-rich solutions deposit in cavities within volcanic rocks, building up layer by layer over thousands to millions of years.

The orange-red color comes from iron oxide (hematite) dispersed throughout the silica matrix. The concentration and oxidation state of the iron determines the intensity - from pale orange to deep brownish-red. Interestingly, many carnelian specimens are naturally pale and achieve their rich color through heat treatment, a practice that dates back to ancient times. Indian craftsmen have been heating chalcedony in clay pots over fires for at least 4,000 years to deepen the red.

This heat treatment works because it converts yellow iron hydroxide (goethite) inclusions to red iron oxide (hematite), intensifying the color. The process is so ancient and universal that the gem trade considers it a natural enhancement rather than a treatment requiring disclosure.

Carnelian is identified by its translucent orange-red color and waxy luster. It differs from jasper (which is opaque), agate (which is banded), and sard (which is a darker, browner variety of the same mineral with no clear boundary between the two).

At Mohs 7, carnelian is hard and takes a good polish. It has no cleavage and breaks with a conchoidal fracture. When held up to light, genuine carnelian often shows a cloudy translucency with subtle color variations, while dyed imitations tend to show color concentrated along surface cracks.