Below is a comparison of the 4 type materials used in carving stone. Granite is very hard stone and difficult to carve. It is not very suitable for fine detailed carving. Granite comes in a wide variety of colors, and the crystal size can vary from large and coarse to very fine and dense. Granite takes a high polish and holds up very well outdoors.
Marble is moderately hard to work.
It will hold very fine detail. When brought to a high polish, it's crystalline structure sparkles. It does not hold up well outdoors and acid rain can begin deteriorating the surface in a few years. Sandstone is formed from sedimentary sand held together by silica or calcium carbonate. Sandstone also has a distinct bed direction, and large chips can be taken off when going with the bed.