 Beryllium is a steel gray and hard metal that is brittle at room temperature and has a close @-@ packed hexagonal crystal structure . It has exceptional stiffness ( Young 's modulus 287 GPa ) and a reasonably high melting point . The modulus of elasticity of beryllium is approximately 50 % greater than that of steel . The combination of this modulus and a relatively low density results in an unusually fast sound conduction speed in beryllium – about 12 @.@ 9 km / s at ambient conditions . Other significant properties are high specific heat ( 1925 J · kg − 1 · K − 1 ) and thermal conductivity ( 216 W · m − 1 · K − 1 ) , which make beryllium the metal with the best heat dissipation characteristics per unit weight . In combination with the relatively low coefficient of linear thermal expansion ( 11 @.@ 4 × 10 − 6 K − 1 ) , these characteristics result in a unique stability under conditions of thermal loading . 
