Chalk

Chalk,
Wastes away with each knock.

Leaving marks on your smock,
I am very limited stock.

As unique as a vintage frock,
It will only come to a shock.
When I vanish and leave a pock,
With beauty like the feathers of a peacock.

So knock and knock and knock.
I will surely block.

But I'm Not firm like a rock,
For I wander, I walk.