Pyroxenes are a major group of rock-forming minerals. Scientists investigated the iron ion status of a calcium-rich pyroxene, using Mössbauer spectroscopy on thin sections of single crystals. The study revealed that in pyroxene crystals consisting of roughly 50% calcium, the tensor that determines the ratios of iron ions at the Mössbauer spectral peaks in the M1 sites — one of two types of cation positions in the pyroxene crystal structure — is independent of the iron content but dependent on the calcium content. The research findings have clarified one of the physical properties of pyroxenes, facilitating detailed future analysis of iron using Mössbauer spectroscopy on mineral flakes.