Carnelian

Hardness: 6.5-7 on the Mohs scale. Color: Translucent reddish-brown to orange-red. Luster: Vitreous (glassy) to waxy. Crystal Structure: Trigonal, but typically massive and cryptocrystalline (crystals are too fine to be seen without high magnification). Specific Gravity: 2.58-2.64. No distinct cleavage, exhibits a conchoidal fracture.

Carnelian is a form of chalcedony, a microcrystalline variety of quartz. It forms from silica-rich solutions that precipitate in cavities of volcanic, sedimentary, or metamorphic rocks, often within geodes or as vein fillings. The reddish-brown to orange color is due to the presence of iron oxide impurities. Its formation is generally secondary at low temperatures and pressures. Geological age varies widely depending on the host rock.

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

Carnelian has been used since antiquity, with significant historical importance in ancient Egypt, Rome, and Greece. It was often used for seals, signet rings, and intaglio carvings due to its durability and the way wax does not stick to it. In the Middle Ages, it was believed to ward off evil and purify blood. It's often associated with courage and vitality.

In the field, carnelian can be identified by its distinctive reddish-orange to brown color, waxy to vitreous luster, and its hardness (it will scratch glass). It typically appears as nodules or in vein fillings. It's often found in association with other chalcedony varieties, agates, and jasper in volcanic regions, alluvial deposits, and weathered sedimentary rocks. Major sources include India (especially the Deccan Traps), Brazil, Uruguay, Madagascar, and parts of the United States.