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In some cases, felsic volcanic rocks may contain phenocrysts of mafic minerals, usually hornblende, pyroxene or a feldspar mineral, and may need to be named after their phenocryst mineral, such as 'hornblende-bearing felsite'. The chemical name of a felsic rock is given according to the TAS classification of Le Maitre (1975). However, this only ...
Hornblende is a complex inosilicate series of minerals. [6] It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rocks. The general formula is (Ca,Na) 2−3 (Mg,Fe,Al) 5 (Al,Si) 8 O 22 (OH,F) 2.
The minerals present in a granulite will vary depending on the parent rock of the granulite and the temperature and pressure conditions experienced during metamorphism. A common type of granulite found in high-grade metamorphic rocks of the continents contains pyroxene , plagioclase feldspar and accessory garnet , oxides and possibly amphiboles .
Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite, diopside, hypersthene, bronzite or enstatite. Pyroxenites are classified into clinopyroxenites, orthopyroxenites, and the websterites which contain both types of pyroxenes (see diagram below).
Quartz monzonite is an intrusive, felsic, igneous rock that has an approximately equal proportion of orthoclase and plagioclase feldspars. It is typically a light colored phaneritic (coarse-grained) to porphyritic granitic rock. The plagioclase is typically intermediate to sodic in composition, andesine to oligoclase.
They are characteristically felsic. The feldspar component of syenogranite is predominantly alkaline in character (usually orthoclase ). For example, the syenogranite in the Salmon Mountains in Idaho is pink to tan and composed of 45–55% alkali feldspar, 15–20% plagioclase , 15–20% quartz , 5–8% biotite , 3–5% hornblende , and ...
Because episyenitization usually takes place in granitoid rock and usually involves alkaline metasomatism (addition of alkali metal oxides to the rock) the result is a rock that has the mineral composition of an igneous syenite. [11] In addition to rare earth elements, [10] episyenites may be important sources of uranium [12] and other valuable ...
Appinites — often synonymously used for hornblende diorites — are a coeval rock suite of plutonic or subvolcanic igneous rocks with variable chemical compositions, covering ultramafic to felsic igneous rocks. They are characterized in all their lithologies by euhedral hornblende crystals as the dominant mafic mineral.