Answer:
Sometimes black, sometimes white, I have veins but no blood
What is lighter than what it is made of?
Three lives have I. Gentle enough to soothe the skin. Light enough to caress the sky. Hard enough to crack rocks.
What force and strength cannot get through. I, with a gentle touch, can do. Many in the street would stand. Were I not a friend at hand.
My sides are firmly laced about, Yet nothing is within; You'll think my head is strange indeed, Being nothing else but skin.
If it’s information you seek, come and see me. If it’s pairs of letters you need, I have consecutively three. What am I?