Cobalt is a Block D, Group 9, Period 4 element. The electronic configuration is [Ar] 3d⁷ 4s². In its elemental form cobalt's CAS number is 7440-48-4. The cobalt atom has a radius of 125.3.pm and it's Van der Waals radius is 200.pm. Cobalt has a metallic permeability two thirds that of iron. It exists as a mixture of two allotropes over a wide temperature range. The transformation is slow and accounts in part for the wide variation in the physical properties of cobalt. It is alloyed with iron, nickel and other metals to make Alnico, an alloy of unusual magnetic strength with many important uses. Samarium-cobalt is one of the highest strength magnet alloys known. Cobalt compounds produce a brilliant and permanent blue color in ceramic glazes, glass, pottery, tiles, and enamels. Co-60 is useful as a gamma ray source. Cobalt is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder.