[Method T]

It should also be noted, Sand and Metal magic have no means to grow on their own, unlike some of the other more expensive trees. (Cosmic, Holy, Occult, Etc.) As the two trees have four spells each, and no hidden spells to work towards. So, you're forced to use some other tree to fill in the remaining 8 slots on your hotbar, and to get a decent aura from.

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They're stupendously expensive for such specialized/restrictive trees.