The correct use is actually "different from". However, you will find "different than" commonly being spoken across the US. This does not mean it is correct.
Different from is correct. Consider saying 'This marble differs FROM this marble' and apply it to different. 'Different than' is an Americanism. However, it's preferable to the heinous 'different...
Different from is correct. Different than is not correct, although it is very common The mistake is made by analogy with the comparative form, which does use than. We say, for example, these books...