Red sand is often used inaluminum and the main content of the red sand: silicon dioxide of 79.4%, ferric oxide of 1.48%, of 10.55%, calcium oxide of 0.85%, magnesium oxide of 0.52%, refractoriness of 1440，silt content of 3.06%,loss on ignition of 1.98% . Red sand with high silicon ，it has advantages of better breathability , high refractoriness, low moisture，etc.
The red sand will be used inand casting sand shall be satisfied the following requirements:
-It has higher purity and cleanliness and takes silica sand for example,requirement ofwith sand is content of SiO2must be over 90%，equirement of larger is content ofSiO2 must be over 97%.
-It has high refractoriness and thermal stability.
-Not easy to be wetting by liquid metal.
-Cheap and easy to get.
Generally speaking ,there are three kinds of shapes of casting sandwith particle shape
-Rounded sand : particle is round or close to round， surface is bright and clean, there are no prominent edges and corners.
-Angular sand: particles turned into a polygon and most of them areobtuse angles
The passage above talks about red sand used in sand casting aluminum.