Answer:
I have thirteen hearts but no body or soul.
I am pronounced as one letter, written with three. I come in blue, black, brown, or grey. Reverse me and I read the same either way. What am I?
By myself, I'm practically nothing. Worthless as a leader, but when I follow a group, their strength increases tenfold. What am I?
Flat as a leaf round as a ring. I have two eyes but can't see a thing.
I dig out tiny caves and store gold and silver in them. I also build bridges of silver and make crowns of gold. Sooner or later everybody needs my help yet many people are afraid to let me help them.
It has no top or bottom, but it can hold flesh, bones, and blood all at the same time.