Literally: flow – metal – melt* – stone
Alternately: Incredible heat. Hot enough to soften and melt metal, or even stone.
Notes: Bear in mind that there are multiple characters that can be rendered in English as “melt.” 鑠 specifically refers to heating up a metal-bearing ore into a molten state, as opposed to the more general 溶, or 熔, which refers to metal being heated to a liquid state.
A synonymous phrase replaces 鑠石 with 焦土 (shou do), “char – earth.”
This phrase comes from our friend the Songs of Chu (Japanese 『楚辞』 = So ji). It seems that the world once had ten separate suns, which appeared in the sky in turn. But one day they all came out at once, producing enormous heat and causing severe harm and damage on the earth below. The divine archer Hou Yi shot them down one by one, and only the last sun was spared in order to carry on normal sun-work.
Little did the heroes of old know that even just one sun would be quite enough to melt the earth’s stone and metal on its own… after humanity was betrayed by a group of robber-barons who poisoned the sky itself for the sake of their personal greed.