Crystal
A blue blade with two different hardnesses in the same crystal, depending on which way you scratch it.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Kyanite has a property almost no other mineral shares in so obvious a form: its hardness depends on direction. Scratch along the length of a blade and it gives at about 4.5; scratch across it and you need something closer to 7. The old name disthene, two strengths, records exactly this. It is one of three minerals with the identical formula Al₂SiO₅ — the others being andalusite and sillimanite — which crystallise differently according to the pressure and temperature they form under, making the trio useful to geologists as a record of what a rock has been through.
The name is from Greek kyanos, dark blue, and the blades really are blue, often with a paler or white streak along the centre. Nepal and Brazil produce the best-known material. Industrially it goes into refractory ceramics, because it expands when heated and holds its form.
Practice associates it with alignment and with speaking plainly, and — like selenite — with not needing to be cleared. It is another stone whose lore is entirely modern, and the directional hardness has been picked up as a metaphor for approaching a thing from the right angle. That is a metaphor, and a good one, and it is not evidence of anything.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Common in contemporary practice
Held along its length rather than across, the blade lying in the palm. The directional hardness gets read as a lesson about approach — that a thing which resists one way yields another — and practitioners are usually candid that this is an image rather than a mechanism.
Carried forward
Common in contemporary practice
Grouped with selenite as a stone that does not accumulate and therefore does not need clearing. The two claims arose separately and neither has a source anyone can point to, which has not slowed either down.
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.