Gemstone Yoni Eggs sells GIA certified crystals! They're a great company.
IIRC, all crystals are technically "porous", though a quick google search reveals that that's a pretty bold thing to say. As long as you clean them before + after use with a natural unscented soap like Dr. Bronners liquid soap, you should be fine. I'd be a little more wary if you have immunity issues or an imbalanced vaginal flora... But I'd tell somebody to be wary of that if they were to have regular ol' sex.
But yeah, don't buy if it's not GIA certified.
learner in brooklyn is well. upvoting for visibility. meanwhile: this book is amazing and it speaks of the real tantra (not the western view) https://www.amazon.com/gp/product/0989761304/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
The link works for me, it goes to good reads.
Here is the link for the book in amazon: Urban Tantra