The distinction of pyrite from marcasite in nodular growths

Abstract

A recent account of pseudo-meteorites by Dr. L. J. Spencer includes a description of nodules of pyrite ‘popularly thought to be “thunderbolts”’. Dr. Spencer himself collected in 1931 a large number from the Lower Chalk outcropping on the foreshore below ‘The Warren’ at Folkestone, Kent. Some of these show well-developed octahedra 5 to 10 ram. across on the outer surface, undoubtedly to be referred to pyrite. More commonly the nodules exhibit small distorted octahedra which might easily be mistaken for marcasite. Indeed, in the past, many of these nodules from the Chalk at Folkestone and elsewhere, have been named marcasite, and they were so labelled in the British Museum collection. Dr. Spencer, therefore, suggested that modern methods should be applied to those cases where the crystalline form is distorted or shOt sufficiently developed to serve as a means of distinction between pyrite and marcasite. The methods suggested in his paper are (1) X-rays, (2) polarized light reflected from polished sections of nodules.