Like Marble, slate is a metamorphic rock. However, slate is created by the alteration of shale or mudstone. Slate is composed predominately of clay minerals or micas that undergo metamorphism. Slate is a popular option for both indoor and outdoor spaces. Commonly used in the foyer, kitchen, walls, backsplash, or fireplace hearths, slate can also be used for outdoor patios or decks. Slate is low-maintenance and a great option to stay within budget means.