Answer:
There are millions of me. I am very small but when moving fast I am deadly.
You use it between your head and your toes, the more it works the thinner it grows.
The ones who see it may go blind, Contracting the fool's madness. You have to dig to find it, Crush big stones or mine it. Wash dirt clumps in a pan and wait for it to settle, A shiny, precious metal.
You’ll have me at night and if you remove the first letter I denote the top, such as on a train
What has 4 eyes but can’t see?
When is it bad luck to see a black cat?
Difficult
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?