On nettles, they're trichomes[1]. Probably somewhat similar to a skin tag? So it deactivates them by weakening the cell wall, just like when you cook the rest of the plant down.

>Both trichomes and root hairs [...] are lateral outgrowths of a single cell of the epidermal layer.

[1]https://en.wikipedia.org/wiki/Trichome

The mineralization is just on the tips of the trichomes.

When dry they are irritating if rubbed against the skin but not stingy anymore and when boiled they have at most a sandy nature as the trichomes soften and can't penetrate as well.

I would assume it denatures the chemicals the sting delivers