A glass-bearing dolerite, which consists of orthopyroxene phenocrysts (γ 1·689, α 1·678, β 1·680, 2V_α 81°, S.G. 3·35) and a glassy mesostasis (n 1·568, S.G. 3·25), is described petrologically. Three new chemical analyses are given. From the petrological and chemical data it can be concluded that the orthopyroxene formed under intratelluric conditions and probably under high pressure. According to the recalculated chemical analysis of the orthopyroxene 0·22 Al³⁺ is in the Y position and much less Al³⁺ in the Z position. The chemical analysis of the residual glass is compared with similar residual glasses, and it shows that iron enrichment characterizes the earlier stages of crystallization differentiation, whereas the later stages are marked by an increase in Si⁴⁺, K⁺, and Na⁺.