Crystal
Quartz darkened by the ground it grew in — Scotland's cairngorm, and the gentlest of the grounding stones.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Smoky quartz owes its colour to aluminium impurities that have been altered by natural radiation from the surrounding rock over very long periods — which means, in a fairly literal sense, that the stone records the granite it grew in. Some material on the market has been darkened artificially by irradiation, and the artificial stones tend towards an even, almost black brown that natural ones rarely manage.
In Scotland it is cairngorm, after the mountains where it was collected, and it has a real and documented place in Highland dress: set in the pommel of a sgian-dubh or a brooch, valued through the nineteenth century, and briefly the object of a Victorian collecting mania after the fashion took hold at Balmoral. That is one of the few pieces of European crystal lore with a paper trail rather than an attribution.
Practice treats it as the mild grounding stone — the one recommended when black tourmaline or obsidian feel too severe. The stated distinction is that smoky quartz absorbs rather than repels, which is a difference nobody has any way of testing but which practitioners describe with unusual consistency.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Common in contemporary practice
Offered as the first grounding stone for people who find obsidian and black tourmaline too blunt. The distinction practitioners draw is between a stone that absorbs and a stone that turns things away; whether the distinction corresponds to anything is unanswerable, but it is described the same way by people who have never met.
Carried forward
Common in contemporary practice
Held at the end of a working day, on the reasoning that it takes the residue of the day rather than adding anything. This is the closest the tradition comes to a stone with a job description.
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.