Crystal
Two different minerals under one word, tougher than steel to break, and central to more than one civilisation.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Jade is two minerals. Nephrite is a felted mass of amphibole fibres; jadeite is a pyroxene, and the two were not distinguished until a French mineralogist separated them in 1863. Both are extraordinarily tough — not hard, which is a different property, but resistant to fracture, because the interlocking fibres have to be pulled apart rather than cleaved. That toughness is why jade was worked into axes and adzes across the Neolithic world, including in Britain, where Alpine jadeitite axeheads were traded across Europe six thousand years ago and deposited unused, apparently as offerings.
Chinese working of nephrite goes back at least to the Neolithic Liangzhu culture and continues unbroken; Mesoamerican jadeite from the Motagua valley in Guatemala was worked by the Olmec and the Maya. The English word comes by an odd route from Spanish piedra de ijada, stone of the flank, from a claim about its use that this compendium does not repeat.
Pounamu, the New Zealand nephrite, carries meaning in Māori tradition that is specific, living and not offered for general use; it is not ours to relay, and the correct thing to do here is to say so and stop. What can be said generally is that jade's reputation for constancy and long keeping is remarkably consistent across cultures that had no contact, and that the toughness of the material is doing some of that work.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Common in contemporary practice
Kept for a long time and passed on, rather than acquired for a working and moved on from. The material rewards this — jade takes a soft, deepening polish from handling that no machine finish matches, so a piece carried for decades genuinely looks different from one bought yesterday.
Carried forward
Common in contemporary practice
Widely sold under names that are not jade at all: serpentine as new jade, dyed quartzite as Malaysia jade, and aventurine as Indian jade. None of these are jade, and only the price usually says so.
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.