Mix and Match

This is a puzzle I've created for fun and enjoyment.The object is to match the pairs of rocks that are the same. Granted that they all look different,but I have changed a basic element in all but four of them. I have inverted the colors or have modified them in some way in Photoshop to make them appear different. I will give you a starting hint... row 2, number one and four are the same rock.Okay, now see if you can guess the remaining eight pairs.Check back on my next post to see if you got them all. Now click on the picture itself for a larger view of the rocks.