I experienced the same thing.Like me, you may have mined some of the gems you have in your inventory and forgotten that you mined them. Those gems do not count. Once you *collect* 10 different types of gems (with no help from the miner) then you will get the achievement.
Hey I have similar problem. I bought a pink heart cut diamond from the consignment shop and I went to deliver it to the science building but everytime I do my sim just walks back out of the building with the gem still in its inventory and the oppourtunity isn't completed. I've tried taking it out of his inventory then placing it back and going to deliver it, I've done it in the day and also at night. Nothing seems to work, a little help would be much appreciated