The commercial particles are all similar in composition, varying primarily in the fractions of alumina, silica, and iron oxide content. Generally, proppants containing more alumina are mechanically stronger, and those with a higher iron oxide fraction are darker in color . In addition to the major components listed in Table 1, CARBOHSP was found to contain minor components (less than 0.05%) of K2O, CaO, MgO, Na2O, MnO, and P2O5 by ICP-MS. The cost of these materials, in quantities greater than 18,000 kg, ranges from ∼$0.6/kg to $1.1/kg with particles having less alumina content (e.g., less mechanical strength) generally being the least expensive . All of the materials are available in a range of diameters between 100 μm and 1000 μm.