microdiorite Petrol.
(maɪkrəʊˈdaɪəraɪt)
[f. micro- + diorite.]
(See quots. 1920, 1961.)
| 1920 A. Holmes Nomencl. Petrol. 157 Micro-, a prefix commonly added—..(2) to the names of phanerocrystalline rocks to indicate a microcrystalline rock or ground-mass of corresponding mineral composition and texture; e.g., microgranite, microdiorite, microsyenite, etc. 1961 J. Challinor Dict. Geol. 127/1 Microdiorite, the medium-grained equivalent of a diorite, usually porphyritic (diorite porphyrite, or porphyrite). 1963 D. W. & E. E. Humphries tr. Termier's Erosion & Sedimentation iv. 94 (caption) The eroded surface of a microdiorite dike. 1965 G. J. Williams Econ. Geol. N.Z. x. 150/1 Positive nickel reactions are also produced by many of the less basic rocks from the ‘mineral belt’ such as the gabbros, leucogabbros and quartz microdiorites. |