Strange rocks obtained by training Crafting are part of the Dahmaroc statue. Two Strange rocks from each skill are required to complete the statue, which can be built once per week. Strange rocks may be stored inside a statue collection bag.
Making gold jewellery (best is to make gold bracelets); making items from leather or dragonhide; making molten glass in a furnace (as well as blowing it into glass objects); shaping clay on a potter's wheel (but not firing clay); making slayer rings; spinning items on a spinning wheel; crafting any type of battlestaff; blowing potion/crystal flasks; playing the Harps in Prifddinas; weaving at the loom in a Clan Citadel.
Crafting silver jewellery and using protean hides will not yield strange rocks.