Cupalite forms dendritic, rounded or irregular grains, typically below 0.1 millimeter in size, which are intergrown with khatyrkite. They have an orthorhombic crystal structure with a yet uncertain space group and the lattice constants a = 0.695(1) nm, b = 0.416(1) nm, c = 1.004(1) nm, and 10 formula units per unit cell. Their Mohs hardness is between 4 and 4.5 and Vickers hardness is in the range 272–318 kg/mm2 for a 20–50 gram load.[6]
Cupalite and khatyrkite are accompanied by spinel, corundum, stishovite, augite, forsteritic olivine, diopsidic clinopyroxene and several Al-Cu-Fe metal alloy minerals. They are remarkable by containing micrometre-sized grains of icosahedrite, a naturally occurring quasicrystal – aperiodic, yet ordered structure. The quasicrystal has a composition of Al63Cu24Fe13 and icosahedral symmetry. The presence of unoxidized aluminium in cupalite and association with the stishovite – a form of quartz which forms exclusively at high pressures of several tens GPa – suggest that cupalite is formed either upon meteoritic impact or in the deep earth mantle.[4][7]