紅玉髓

Carnelian is a warm orange to red-brown variety of chalcedony — the microcrystalline form of quartz. Its glowing colour comes from finely dispersed iron oxides, and it has been treasured for jewellery, signet rings and carved seals since the ancient world.

Identifying carnelian

Carnelian is hard (about 7 on the Mohs scale, like all quartz), translucent, and takes a high polish. Its colour ranges from pale orange through deep red-brown; darker, browner material grades into the related variety sard. Natural carnelian often shows a cloudy or banded distribution of colour, while heat treatment — an old and accepted practice — can deepen pale agate into rich orange.

Where it is found

Fine carnelian comes from India (notably the Deccan basalts of Gujarat), Brazil, Uruguay, Madagascar and many other places where silica-rich fluids filled cavities in volcanic and sedimentary rocks.

For collectors and lapidaries

Even, glowing colour, translucency and freedom from fractures give carnelian its value — both as polished cabochons and beads and as natural nodules showing rich colour.