Crystal
Feldspar full of tiny metallic platelets that throw back the light in flecks — schiller, not colour.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
The glitter in sunstone is called aventurescence, and it comes from thousands of microscopic plate-shaped inclusions lying parallel inside the feldspar, each one catching the light at the same moment as the stone is turned. In most Indian and Norwegian material the platelets are hematite or goethite. In Oregon sunstone they are metallic copper, which is geologically unusual — the copper was dissolved in the lava the crystals grew in — and gives stones that run from clear through peach to a deep red, sometimes with distinct colour zones in a single crystal.
The name is straightforward and the correspondences follow it: solar, projective, warming. Practice sets it opposite moonstone, which is the same mineral family doing something quite different with light, and the pairing is common enough that the two are often sold together.
The Icelandic sagas mention a sólarsteinn used for navigation, and there has been real scientific interest in whether a birefringent crystal could locate the sun through overcast — Iceland spar, a form of calcite, is the usual candidate. That has nothing to do with this feldspar beyond the shared name, but the two get run together often enough to be worth separating.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Common in contemporary practice
Paired with moonstone and carried together, one in each pocket, as a balance of projective and receptive. The pairing is modern, tidy and mineralogically apt in a way its inventors probably did not intend — both stones are feldspars, differing chiefly in what is trapped inside them.
Carried forward
Common in contemporary practice
Reached for in the dark months. Practitioners are generally clear that this is about wanting something warm-coloured in the hand in February, and are not inclined to dress it up further.
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.