Metals (and beasts) represent the hard (exacting, aggressive, unyielding) force of the proxy governments of Satan on Earth.

We see this in the image of the prophecy of Daniel 2. The head of gold represented the kingdom of Babylon and this entire system of church and state under the leadership of Satan is referred to as "Babylon".

Thou [King Nebuchadnezzar] art this head of gold. And after thee shall arise another kingdom inferior to thee [silver, Media-Persia], and another third kingdom of brass [Greece], which shall bear rule over all the earth. And the fourth kingdom shall be strong as iron [Rome]: forasmuch as iron breaketh in pieces and subdueth all things: and as iron that breaketh all these, shall it break in pieces and bruise. Daniel 2:38-40

So we find in Revelation, speaking of the end of time thousands of years after the head of gold was ended, "Babylon" is still opposing Yahweh.

And a mighty angel took up a stone like a great millstone, and cast it into the sea, saying, Thus with violence shall that great city Babylon be thrown down, and shall be found no more at all. Revelation 18:21

Metal is unlike dust or clay.