Slate is a fine-grained, low-grade metamorphic rock typically composed of clay minerals, often formed from the burial and subsequent metamorphism of mudstone or shale. Its distinguishing characteristic is its perfect fissility, meaning it naturally cleaves along smooth, flat planes, a property that makes it valuable as a roofing material, paving stone, and surfacing veneer. The mineral composition can vary, often including chlorite and kaolinite, and its color ranges from deep gray to green. Geologically, the formation process involves regional metamorphism under increasing pressure and temperature, processes that recrystallize the original sediment and give the rock its characteristic planar structure.