The Petch House's test started with a sample from the countertop slab. Sealant was applied to one half and the other was left as-is for a comparison of sealed and unsealed marble. Then the sample was covered in all kinds of acidic foodstuff and beat up with a dinner knife.
Testing continues here, after the sample has a chance to rest a bit, and final results and observations are here. Thanks to Greg at The Petch House for putting this sample to the test and sharing it all with us.
AT related post: Good Questions: Why Not Do White Marble Kitchen Countertops?.
Top photo: ABKA. Others: The Petch House