There is a total of 170 Lorestones in the original game. With 10 skill points in detect magic, you will be able to see the Lorestones marked on your map.
Usually, except for a few, each set of stones is within a certain area of the map, so when you the message "...set complete" you can progress to the next area.
The trophy unlocks at 170 Lorestones, so if you have done both DLCs(20 Lorestones) you can skip a few in the original game.
Here is Gamesradar's guide, complete with maps of all the stones.
http://www.gamesradar.com/kingdoms-amalur-reckoning-loreston...Have fun!