I have heard that it is not recommended to wear these stones on your left hand.
Yes it is permissible to wear rings on the left hand. Although, there are several reports which favour wearing of rings on right hands, we also have reports that some of the Imams (the frst three Imams) used to wear rings on their left hands. What is not permissible, according to some reports, is wearing rings on the middle finger. God knows the best.
Reference: Shaykh Tabrasiy, Makarimul Akhlaq, chapter titled "fi kayfiyyatut takhattum.", Tehran, 1972. Hasnain Kassamali Humble servant of the Ahlul Bayt (a).