if you have some more of the fabric, make some "test' patches with the chalk on it and see what works, how the fabric is affected by different cleaners and what cleaner takes the chalk out. Be sure to mark the patches so you know which one's which. That way, you don't experiment on the quilt itself. I would try Formula 409 first. I've used that on fabrics with grease spots and it's never bothered the fabric.