Carnelian
Orange-red chalcedony coloured by iron oxide — the stone of Roman signet rings, because hot wax does not stick to it.
Carnelian is chalcedony coloured orange to red-brown by iron oxide dispersed through it. The darker brown-red end is called sard, and the boundary between the two is a matter of judgement rather than of composition.
Much commercial carnelian is heated agate. Heating oxidises iron already present and deepens the colour, and it has been done for a very long time — heat treatment of carnelian is attested in the Indus Valley in the third millennium BC, which makes it one of the oldest deliberate material treatments there is evidence for.
Its classical importance rests on a practical property: hot sealing wax does not stick to it. That made it the seal-stone of the ancient Mediterranean, and a very large share of surviving Greek and Roman engraved gems are carnelian.
How to identify it
Translucent orange to red, waxy lustre, quartz hardness, no cleavage. Natural material tends to show a cloudy or uneven colour distribution; heated agate is often more uniform and shows the parent banding in transmitted light.
Uses
Seals and intaglios historically, and it is hard to overstate how much of the ancient engraved-gem record is this one material. Beads, cabochons and ornamental use since the Neolithic, with carnelian beads traded across enormous distances in the Bronze Age.
Name origin
From the Latin carneus, fleshy, for the colour — reshaped in English by association with cornum, the cornel cherry, which is why both spellings persist.
How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.
How this connects
Where a connection has been confirmed by an outside reference, that reference is named beside it.
is a variety of
- Quartz — mineral · chalcedony coloured by iron oxide, and much of it heated agate — a treatment attested in the Indus Valley in the third millennium BC
contains
- Iron — element · as oxide dispersed through the chalcedony
is used as
- Pigment — application · not as a pigment — recorded because the iron oxide that colours it is the same compound used as one, at a different scale
is commonly confused with
- Agate — mineral variety · carnelian is chalcedony coloured by iron oxide and much of it is heated agate, so the two are the same material at different points of a treatment
Sources
- Material WorldOur own writing
- Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)