How much a really heavy small bed weighs

In stone arms I gather, peace and prayer, wrapped in silence like a nun's gentle care. Tucked away, a quiet retreat, where wise old stories and whispers meet.

I am thirteen letters long, while my definition can be as short as six: ONE HUE. What's my name?

I start as stone beneath the ground, yet end up flat and thin. A roof may wear me overhead, or chalk may mark my skin.

To mail a letter to a friend, Label, stamp, lick and send. They used to use me all the time, But now it seems I'm past my prime.