Not my intention to hijack this thread but until the OP returns (if the OP returns) I think it is noteworthy to expand a little on IRC's above comments.
He is correct, the blades you find at box stores won't generally be properly labeled as to what is used for what. Some may say "marble" and some may say "granite" and some may be labeled with other generic mentions but the truth is the labelling is basically useless, especially to a novice.
Blades are of varying qualities and are manufactured using a few different methods. It is great when you can match a diamond blade to a particular tile product. The tiles (as hard as they are) can cut like butter and the cuts are clean with a proper blade.
Industrial diamonds used in blade making can also be of varying qualities. I have to say that you shouldn't expect much from a diamond blade that costs only $10 or $25 and sometimes even $60 blades can leave a lot to be desired.
Several years ago I made a feeble attempt to launch a campaign to get tile manufacturers to determine which grade diamond blade would best cut their particular product and then to match that blade (by name) to their tile issue at the point of sale. Seems the thing to do to me. Of course that fell on deaf ears and we all still have to wander around trying to cut some miserable-hard tile products with substandard blades. There is hardly any where in the blade industry that a person can actually make an informed decision about which blade to buy for what purpose.
The larger mainstream blade producers have an abundance of information available but now you're into blades that routinely cost 3 to 4 hundred dollars and even a great deal more in some cases. But, they are worth it.