The green and purple slates can run together. The red slate (rarest of all domestic slate) is typically quarried seperate from the green and purple slates. Usually if the quarry wants to quarry predominantly purple slate they will be in a certain part of their quarry, and if they want predominantly green slate they will be in another. When they get into a section where there is a lot of green and a lot of purple running together, that is called mottled green and purple slate. These colors are only quarried/found in a short stretch along the VT/NY border. The traditional grey/black slate used for turkey calls is quarried in PA. I am sure all the slates being used in turkey calls coming from VT/NY, are coming from the same few quarries. When I was in the business right out of college, we would never make call blanks because it just wasn't worth it. You get a ton of breakage Gauging (grinds the slate to a uniform thickness) two faces of a slate down to 1/4in or less. My guess is there is only one, maybe two places making all the red/green/purple slate call blanks available.
