Moonmilk is magical, milky substance on cave walls, formed when moonlight shines into the mouth of the cave or appear further in the cave when moon spirits or creatures with a strong affinity with the moon venture in. The interaction between the moonlight and elemental crystal in rock, whether deposits of ore or fine, ground up flecks that can be seen scintillating in the light lead to the formation of the substance. It can be used in potions for various effects related with moonlight.