|Foundry sands are grainy light-colored minerals, which are suitable for the production of foundry molds and cores. The main requirements are sufficient heat resistance, strength and suitable grain size (medium grain size and optimal grain shape). Natural foundry sands are very variable ,thus being increasingly replaced by silica sands, which are mixed with specified amount of binding agents, typically bentonite. Foundry sands are being divided into several types, depending on the content and nature of fines (grains below 0.02 mm), medium grain size, grain shape and regularity of the chemical composition .Typical foundry sands are sands for casting sand molds for steel castings, special castings of other metals and sands for grey cast iron. In practice there is a distinction between natural foundry sands – usable directly or after minimal processing and silica foundry sands (without clays), which have to be supplemented with bentonite or organic binders to produce moulding compounds.