Hard and crystalline, granite is classed as an igneous rock traditionally made up of quartz and feldspars. Colours can often vary from pinks ( due to the alkali feldspar ) to grays depending on the make up of their chemistry and mineralogy. Though granite has a medium to coarse grained texture to it stones like marble and limestone have a grainer texture to them making them easier to finish grind and polish. Granite is certainly a hard and tough stone to deal with and definetly takes its toll on the tooling we use to machine it.
During the grinding process granite would normally be taken further regarding the finish grinding stages. Marble and limestone can be finished between 400-800 grit and then powder polished/crystallised, where as granite could be taken up to 3000 grit and then crystallised. It is far harder to get a finish on granite, warning are given out by companies like HTC specifically on the subject. One of the problems is the colour of the stones. Many black looking granites can start to turn very slighly pink with grinding and crystallising which could cause a huge amount of upset to a client so caution needs to be taken.
Tikko supply some great products for finishing granite. We use their powder and liquid to crystallise granite and some other chemicals. They leave a great finish but you do have to clean the grout lines afterwards, often with dark floors clients will have dark grout lines and the Tikko's powder and liquid can turn them white.