The inorganic INS K-feldspar and the organic INS Snomax were used as test materials to evaluate this density gradient centrifugation method. Potassium-rich feldspar (K-feldspar) is an important component of atmospheric mineral dust and an effective ice nucleus ). The density of K-feldspar is in the range of 2.55 -2.63 g cm -3 , based on heavy liquid density separation .