From CEDict:
MBP-WWG:~ Admin$ egrep "\t石\t" /Users/Admin/Downloads/cedict_1_0_ts_utf-8_mdbg.txt
石 石 Shi2 surname Shi
石 石 dan4 dry measure for grain equal to ten dou 斗<br/>ten pecks<br/>one hundred liters
石 石 shi2 rock<br/>stone<br/>stone inscription<br/>one of the eight ancient musical instruments 八音[ba1 yin1]
Is the second one an error?
Is this what is meant by "variant readings" in How many Chinese characters have multiple readings/pronunciations in Mandarin? ?