Commentary for Job 28:3

He made an end The Omnipresent [made an end] when there will be darkness, for the heavens shall vanish and the earth shall rot away, and He fathoms the end of everything.

An end is made to darkness and every limit is explored by the diviner’s black stone.¹⁶A stone which detects the presence of metals. Malbim adds:
It is a stone of which the ancients said that whoever possesses it can divine where various metals can be found in the bowels of the earth. It is a stone which attracts metals just as magnetic stone [lodestone] attracts iron.

a stone A stone whence darkness and the shadow of death emanate. A stone is the place of the source of trouble. For this reason, a place of trouble is called a stone, like a man who dashes his foot against a stone, who suffers pain. So I heard. This is like (Isa. 34:11), “a line of waste and stones of destruction”; (Dan. 2:45), “that from the mountain a stone was cut.”