Crystal
Warm orange chalcedony — the seal-stone of the ancient world, because hot wax will not stick to it.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Carnelian is chalcedony — quartz in fibres too fine to see — coloured orange to blood-red by iron oxide. Much of the material on the market is agate that has been heated, a practice attested in India for a very long time and not a modern deception; the Gujarat trade was baking carnelian in the sun and then in ovens well before Rome had a use for it.
Its great practical virtue in antiquity was that hot sealing wax does not adhere to it, which made it the standard stone for signet rings and scarabs across Egypt, Mesopotamia, Greece and Rome. That is an enormous number of surviving objects, and it means carnelian is one of the stones we can say most confidently that ordinary people handled every day. Roman intaglios in carnelian turn up in Britain by the hundred.
Practice reads it as warmth, appetite and momentum — the stone for beginning something rather than finishing it. Its placement at the sacral centre is a modern arrangement, but the older lore points in a compatible direction, and for once the two do not have to be forced together.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Pliny the Elder, Natural History, Book 37 (c. 77 CE)
Pliny says the sarda takes its name from Sardis, where it was first found, calls it the commonest stone of all and the one most used for engraving, and notes that it was long the most familiar gem in Rome. He is describing a material so ordinary that its ubiquity is the fact worth recording.
Carried forward
Common in contemporary practice
Carried at the start of a project rather than through it. Practitioners describe carnelian in the language of ignition — useful for getting going, less so once you are — and it is one of the few correspondences that survives contact with people who actually keep notes.
Credit what you carry. Much of this comes from living traditions, and some of it from traditions that are closed — held by particular peoples and not offered for general use. Where you know whose practice a reading came from, name them; where you don't, say that too.