This spell turned a small stone into a magical incendiary missile. When held in the sunlight, a regular stone became so hot that it glowed with heat but did not harm the caster.
The sun stone was aimed at a target like a magic missile. If the stone missed its target then it fell to the ground where it was still hot enough to damage anything touching it for several minutes. Wizards were capable of casting multiple sun stones at once depending on their magical might. Each sun stone had its own target.
This spell required a small stone to cast.