Chromian spinel in volcanic rocks is a potential discriminant for magma chemistry. The TiO₂ content of spinel, compared at similar Fe³⁺/(Cr + Al + Fe³⁺) ratios, can distinguish island arc basalts from intraplate basalts. MORB spinels are low in this ratio and are intermediate for the TiO₂ level at comparable Fe³⁺ ratios. Spinels from back-arc basin basalts, although similar in TiO₂/Fe³⁺ ratio, are more enriched in Fe³⁺ than the MORB spinels. Spinels in the oceanic plateau basalts are distinctly lower in TiO₂ than other intraplate basalt spinels and even slightly lower in TiO₂ than the MORB spinels. The data were successfully applied to estimate the kind of the magma from which spinel-bearing cumulates, especially dunites, were formed. Original magma chemistry of altered or metamorphosed volcanics in which spinels survive can also be estimated by the chemistry of relict spinel alone. It is possible to estimate the magma type of source volcanics for detrital spinel particles of volcanic derivation.