Course, medium, and fine; marking the passage of time; I wear, polish, and grind.

I have a slender waist and two clear bellies, But hold no drink, nor whisper any tellies I'm flipped and turned, a steady measure, Of moments fleeting, of joy of pressure.

I have a twin, but I do not have a sibling. I am known for my warmth.

I hide the sun and shield the rain, fold me up to ease your strain; what am I?

My flavor's good for the soul, but my purpose's not always to be eaten. My work's good for the sole, especially when you walk the path less beaten.