Mindful writing can be very calming when we are feeling stressed or anxious. Although I believe the idea of “small stones” is for them to be both mindful and poetic, mindful writing need not always be poetic or beautiful. For example writing a detailed description of a scene, a picture or an object is writing mindfully and is calming for the mind even if the writing turns out to be distinctly un-poetic.
Have a go … choose an object you love and write a detailed description of it. Try to include some (or all!) of the 5 senses in your description.