The cut edge is probably sucking up water from the machinery used to cut it. Give it a week or so and see if it dries and/or hit it with a Bernz-O-Matic torch. Quartzite is notorious for incomprehensible staining. Search this site, please.

Thanks I did search but was having trouble finding a comparable situation. I’m just so confused because it was cut off site a week before being installed. I am trying to figure out if the contractor who installed it did something that damaged the stone.