Natural stone according to its generation factor and derivation numerous kinds, more general classification is stone divides into sandstone, slate,marble and granite four big kinds.SLATE is a kind of metamorphic rock with plate structure and almost no recrystallization. The original rock is argillaceous, silty or neutral tuff. The color of SLATE varies with the impurities it contains. Carbon is black or grey; Calcium - containing hydrochloric acid will bubble, so the general classification of its color, such as green SLATE, black SLATE, calcium SLATE.