There are at least 5 stained/bleeding quartzite horror threads here and brace yourself for very bad news. There is no cure and the industry doesn't care a whit.

I have a similar issue. Did you have get any resolution?

We are shopping for quartzite now. Can you share the name of this stone that had this problem? And has the cause been determined?

Any one can call a stone what ever they want realistically. You need to get a sample piece of your choices and test them yourself.

Avoid Mont Blanc