BS 6088A Physics and chemistry function Item Standard Specific gravity g/ cm3 2.4--2.6 Refractive index e1.5 Spherical beads ( % ) > 70 The Sieve Analysis Diameter ( ¼ m) Standard Retain ( % ) > 1180 0-3 1180--850 5--20 850--425 65--95 80 The Sieve Analysis Diameter ( ¼ m) Standard Retain ( % ) > 850 0-5 600--850 5--20 300--600 30--75 180--300 10--30