Metal salesmans sample.
An example of the element Tantalum

This auction is for a very unusual, what I think would be called a Salesman Sample, of 5 exotic metal disks. The brown plastic case that measures 2.50 in. by 6 in., was received by my Father when he visited the Kawecki Berylco Industries in the 1970's. The company was bought by Cabot Corp. in the late 70's. The disks measure 1.25 in. dia. by .1in. thick. According to the description in the case the 5 metals are Beryllium, Lockalloy, Beryllium Copper, Columbium [an older name for niobium], Tantalum.