Crystal
Not moss and not really agate — mineral ferns grown inside clear chalcedony, and the gardener's stone.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
The green and black fronds inside moss agate are not fossils and not plants. They are dendrites: branching mineral growths, usually of manganese or iron oxides, sometimes of chlorite, that crystallised into the silica as it formed. Dendrites branch the way they do for the same mathematical reasons that frost and river deltas and lightning do, which is why the result looks so persuasively organic to an eye trained on living things.
The name is doubly inaccurate, since true agate is banded and this material is not; mineralogically it is a dendritic chalcedony. The classic sources are India and the Yellowstone River gravels of Montana, where the stones are collected as waterworn cobbles rather than mined.
It is the stone practice most consistently associates with growing things — kept in a greenhouse, buried at the corner of a bed, given to someone starting an allotment. That association is not ancient and appears to be a straightforward reading of the picture, which is fine as far as it goes. Where it becomes more interesting is that the stone is also widely used for slow work of any kind: not the beginning of a thing but the long unglamorous middle of it, which is closer to how gardening actually feels.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Common in contemporary practice
Buried at the corner of a bed or kept among seed packets. The custom is recent and openly analogical, and it survives partly because it is one of the few crystal practices that puts a stone somewhere it will be forgotten about — which practitioners sometimes say is the point.
Carried forward
Common in contemporary practice
Used for work that takes a long time and shows nothing for most of it. This reading has less to do with the greenery and more with the fact that dendrites record a slow process — an argument about patience made from geology rather than horticulture.
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.