diorite
/ˈdʌɪərʌɪt
/noun [mass noun] Geology
A speckled, coarse-grained igneous rock consisting essentially of plagioclase, feldspar, and hornblende or other mafic minerals.The thrust sheet overlying the Delaney Dome Formation is composed of the basic Ballyconneely Amphibolite and interbanded quartz diorite and hornblende gneiss that intrude the Dalradian sediments....
- It is dominated by variably foliated, medium-grained, even-textured to porphyritic biotite hornblende tonalite and quartz diorite.
- The clasts range from angular to subrounded and show a weak preferred orientation when elongate; they include micaceous siltstone, fine-grained sandstone, tuffaceous rock, andesite and medium-grained diorite.
Derivatives
dioritic
- Like the Kevins Dam suite, these granites may also be derived from melting of quartz dioritic to tonalitic rocks.
- A dioritic pod in varitextured gabbro was sampled for U-Pb age determination.
- Numerous undated granitic and dioritic plutons intrude the Palaeozoic rocks and form large areas of Karlik Tagh and Barkol Tagh.
Origin
Early 19th century: coined in French, formed irregularly from Greek diorizein 'distinguish' + -ite1.