Aries,
Sand would not be the first choice. The small uniform grain sizes do not 'rake' well and the color does not provide the soothing effects you are looking for. The material of choice is crushed granite and is actually easier to come by than you might imagine. Most farm feed stores carry it in several grades as turkey grit. Also known as 'chicken grit'. The irregular grain shapes are the right size and texture to allow for easy, long lasting raked patterns and the color and luminosity make for a contemplative image. Such a nice gesture for your father. Have fun!

Greg