Carnelian

Mohs Hardness: 6.5-7. Color: Various shades of red to reddish-brown. Luster: Vitreous to waxy. Crystal Structure: Trigonal (microcrystalline quartz). Cleavage: None. Fracture: Conchoidal. Specific Gravity: 2.58-2.64. Carnelian is typically translucent to semi-opaque.

Carnelian is a cryptocrystalline variety of quartz (SiO2), specifically a form of chalcedony, colored by impurities of iron oxides. It forms from silica-rich solutions percolating through volcanic rocks, hydrothermally deposited in cavities, or in sedimentary environments. Its formation is generally not tied to a specific geological age but occurs where the necessary silica and iron oxide solutions are present.

Primarily used as a gemstone in jewelry (cabochons, beads, carvings). Also used for ornamental objects, seals, and intaglios. Historically, it was used for signet rings and amulets.

Carnelian has been used since antiquity, with archaeological finds showing its use in jewelry and seals dating back to the Bronze Age in the Near East. It was highly valued by ancient Egyptians, Greeks, and Romans, often associated with protection and courage. The intensity of the red color in carnelian can sometimes be enhanced by heat treatment.

In the field, carnelian is identified by its distinctive red to reddish-brown color, its translucent to semi-opaque nature, and its waxy luster. It often occurs as nodules or in veins within host rocks. It can be distinguished from other red minerals by its hardness (scratching glass) and lack of cleavage. Common localities include India (especially near Poona and Cambay), Brazil, Uruguay, Madagascar, and parts of the United States (e.g., Oregon). When collecting, look for specimens with good color saturation and translucency. Be aware that some carnelian on the market may be heat-treated agate to enhance its color.