Normal Earth Runes need a Earthstone along with a Blank Rune; a Silver Ingot and three Weak Earth Runes to make one Normal Earth Rune.
Normal Runes can be crafted at level ten at the Rune Altar.
You need three of these to learn Stone Slash and you will need extra to cast the spell.
The command to make a Normal Earth Rune is [nya!rpg rune altar earth]. For more info use [nya!info normal earth rune].