174 * ALBERT JOHANNSEN 



it, by analogy to trachydolerite, for an extrusive rock whose deep- 

 seated equivalent would be intermediate between alkali-syenite 

 and essexite. It represents, consequently, a rock carrying a feld- 

 spathoid or aegirite, riebeckite, etc., and not, as one would suppose 

 from the name, a rock intermediate between trachyte and andesite.) 



(2214) Monzodiorite. The term syenodiorite was proposed by 

 the writer^ for the quartz-free equivalent of granodiorite. For the 

 reasons stated under granodiorite (229), this term is withdrawn and 

 monzodiorite is substituted for it. 



Syn. : Syenite-diorite Brogger.^ 



Andelatite. For the extrusive equivalent of monzo- 

 diorite, the term andelatite, as intermediate between andesite and 

 latite, is suggested. See note under granodiorite (229). 



Mugearite Harker. Mugearite, from the village of 

 Mugeary, is the name given by Harker^ to certain extrusive rocks 

 resembling basalt but with oligoclase (AbyAnz) and much oUvine. 

 A modal analysis shows the rock to consist of oligoclase 57I per 

 cent, orthoclase 12I per cent, olivine, iron ore, and augite (augite 

 quite subordinate to olivine) 26^ per cent, and apatite 3I per cent. 

 It is therefore an olivine andelatite. 



(2215) Diorite Hauy. The term diorite (from Sioptfco, "dis- 

 tinct") was introduced by Haiiy^ as a substitute for Werner's 

 term Grilnstein. The name now stands for a rock consisting of 

 acid plagioclase and a dark mineral. 



Syn. : Griinstein Werner, Diabase Brongniart. 

 Ohgoclase-diorite. 

 Andesine-diorite . 



Andesite von Buch. Formerly there were included, 

 under the name trachyte, not only orthoclase rocks, but those 



'Albert Johannsen, "Suggestions for a Quantitative Mineralogical Classification 

 of Igneous Rocks," Jour. Geol., XXV (191 7), 89. 



^W. C. Brogger, "Die Mineralien der Syenitpegmatitgange der siidnorwegischen 

 Augit- und Nephelinsyenite," Part I, Zeit.f. Kryst., XVI (1890), 49. 



3 Alfred Harker, "The Tertiary Igneous Rocks of Skye," Geol. Surv. Mem. (1904), 

 p. 265; John S. Flett, "On the Mugearites," Summary of Progress, Geol. Surv. 

 (1907), p. 119. 



4 The term first appeared in the publications of some of Haiiy's students. Tl^us 

 see J. F. d'Aubisson de Voisins, Traite de geognosie (Strasbourg and Paris, 1819), p. 146. 

 Later it was used in Abbe Haiiy's Traite de mineralogie (Paris, 1822), IV, 540. 



