Figure F10. Composition of orthopyroxene. A. TiO2 vs. Al2O3. B. TiO2 vs. CaO. For orthopyroxenes, there is no essential compositional difference among the magmatic orthopyroxenes and those of blebs in the intergrowths (near the high-temperature microscopic veins and in the interfingering clinopyroxene), except for grains within the high-temperature microscopic veins in olivine. The latter are characterized by lower contents of CaO, TiO2, and Al2O3 than other orthopyroxenes. These compositional features are attributed to the Ca-, Ti-, and Al-poor nature of olivine, which is a precursor of the orthopyroxene.

Figure F10. Composition of orthopyroxene. A. TiO₂ vs. Al₂O₃. B. TiO₂ vs. CaO. For orthopyroxenes, there is no essential compositional difference among the magmatic orthopyroxenes and those of blebs in the intergrowths (near the high-temperature microscopic veins and in the interfingering clinopyroxene), except for grains within the high-temperature microscopic veins in olivine. The latter are characterized by lower contents of CaO, TiO₂, and Al₂O₃ than other orthopyroxenes. These compositional features are attributed to the Ca-, Ti-, and Al-poor nature of olivine, which is a precursor of the orthopyroxene.