slate

slate, fine-grained rock formed when sedimentary rocks such as shale are metamorphosed by great pressure. Slate splits into perfectly cleaved, broad thin layers; this characteristically regular and planar cleavage is called slaty cleavage. In the formation of slate, pressure causes the flaky minerals within the sedimentary rock, such as mica, clay, and chlorite, to be reoriented; the flat faces of the minerals lie at right angles to the source of the pressure, and the planes of easy cleavage are also at right angles to the source of the pressure. Slate demand in China has expanded 7.3 percent per year over the last decade and reached 2.2 billion square meters in 2005. Demand gains will continue to outpace the global roofing market, rising 4.9 percent annually through 2010 to more than 2.7 billion square meters, benefitting from robust growth in the booming construction industry in China. International roofing product manufacturers and distributors recognize the tremendous market potential that China offers.