Under pressure is the only way I work, and by myself is the only way I'm hurt. What am I?

Question

I never only work one way,
Despite what you normally think.
I came in many shapes and sizes,
And often sit over a sink.
You see me almost everywhere,
Although you may not know.
When you see your reflection
You know it's what I also show.
So tell me now, do you know?
What am I? Can you see?
Read through these very simple clues
And soon you will find me.

Answer 1

RESULT: A diamond.