I believe this was answered earlier in this thread but the backsplash tile is 3x6 Eastern White Marble - sometimes also referred to as "Oriental White" marble.

To address jbtanyderi's comment: There are no hard and fast rules about backsplash heights above cooktops; the goal of course is to provide an easy-to-maintain surface immediately behind the appliance that is heat and stain resistant. In this case, the desire to maintain a consistent rail height won out over concerns about occasional high splatter or grease build-up.