You will need to post a picture. There are several stone experts who will likely comment if you give more information and some photos.

Have you talked to the fabricator and installer? What do they say?

They look natural to me.

Natural fissure. That’s how you know Mother Nature made it, and not man.

Looks fairly normal to me. Can you feel crack when you run your hand over the surface?

yes you can feel the crack when you run your finger across it you can feel the the stuff that they used to fill it in where the crack is.

It’s a reinforced fissure. Not a crack. Mother Nature made. Manmade quartz doesn’t have natural features like that.

They should have made it smooth. Might want to get them back to carefully smooth it out. Not hard to do.