Carnelian is chalcedony, and that single word does most of the explaining. Chalcedony is quartz in its fine-grained form, the same material as agate, and where agate bands in layers, carnelian is the version that is mostly one colour. The orange to red comes from iron oxide in the stone, and the depth of it depends on how much is there and how long it sat in the ground. 

Pale apricot through to a deep, almost blood red, and the stone is translucent enough to catch light at the edges. It sits at six and a half to seven on the hardness scale, which is why it has been used for beads and seals for thousands of years. It is hard enough to be worn against the body for a lifetime without much changing.

One thing worth knowing, because it comes up whenever carnelian is discussed. Most of the deep red material on the market is heat treated. That is not a modern cheat, and it is not the same as dyeing. Carnelian with more iron in it turns from orange to red when it is heated, and the method goes back thousands of years. The same technique was used in the Indus Valley. It is an accepted part of preparing the stone rather than something being hidden, but it does mean the colour of the piece you buy may not be the colour it was in the ground. Where a stone is dyed rather than heated, the colour sits in the cracks, and that is the difference.

The name has an odd history. Carnelian is the modern spelling, from the Latin cornum, meaning cherry, after the colour. The older form was cornelian, and that has stuck so you may find it spelled that way today - it's the same stone. It comes out of India, Brazil, Uruguay, Madagascar, Egypt and Indonesia, and India in particular has worked it continuously since the ancient world. 

An ancient name for it was sard, and there is a separate stone called sardonyx, which is carnelian banded together with white or black chalcedony. Carnelian also fades. A stone left in strong sun for years will lose its depth, and a piece that has been in a bright window will be noticeably paler than one that has been kept in a box.

Traditionally associated with

Carnelian has one of the longer histories of any stone on this site. It is worked into beads and amulets in Egypt from the earliest dynastic period, it is cut into seals and signet rings in Rome, and it turns up in jewellery across the ancient Near East. 

The tradition most often attached to it is the seal. Carnelian was the stone of choice for a signet because wax does not stick to it. It is traditionally associated with the setting of a mark and the keeping of a promise, which follows from that use.

How I'd keep it

Chalcedony is durable and easy. Warm water and a soft brush are fine, and it can be dried with a cloth. Keep it away from acids, bleach and household cleaners, and out of ultrasonic cleaners if the piece is set in silver with stones that might be treated. Because it is hard, keep it clear of softer stones in a drawer, as it will be the one doing the scratching. The one real caution is light. Keep a carnelian piece out of a bright window and out of long spells in strong sun, because the colour fades over time and there is no bringing it back.

What to watch for

Heat treatment is normal, dyeing is not, and the test is the usual one. Look at the cracks and the hollows, because dye pools in those and colour that belongs to the stone runs through it. Look also at the string holes on beads, since dyed beads show colour collected around them. The other stone regularly sold as carnelian is dyed agate, which is the same family and behaves similarly, so the honest question there is whether the colour is natural or applied. Because carnelian is common and cheap, there is no good reason to fake it well, so a piece at a sensible price is usually what it says it is.

In the shop

There is quite a range. If you want to wear it, the Carnelian and Sterling Silver Feather Necklace is the largest piece at £120, and there are the Carnelian and Sterling Silver Stud Earrings at £60, the Carnelian Crown Ring and the Carnelian and Sterling Silver Triquetra Bracelet both at £70, and the Carnelian Ring With Bird Detail at £80. For the altar, the Carnelian Orgonite at £25 is a pyramid of resin set with copper and carnelian.

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