Adding what DD has said before and to answer your queries, that you shouldn't be petrified / stoned through any means under 100 hard mdef equipment sets.
Adding iROwiki links for reference, tbh I never bother to try the petrify effects immunity under 100 hard mdef but by knowing that many knowledgeable iROwiki contributors still updating the page from time to time I'll put my faith on them
Let all of us know in case you found out that the facts is diverged from the status effects mechanics posted in iROwiki for better relevancy and reliability.
Edited by Casval17, 20 June 2018 - 12:51 PM.