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Quartz-porphyry, in layman's terms, is a type of volcanic rock containing large porphyritic crystals of quartz. [ 1 ] [ 2 ] These rocks are classified as hemi-crystalline acid rocks . Structure
Porphyritic texture in a granite. This is an intrusive porphyritic rock. The white, square feldspar phenocrysts are much larger than crystals in the surrounding matrix; eastern Sierra Nevada, Rock Creek Canyon, California. A porphyritic volcanic sand grain, as seen under the petrographic microscope. The large grain in the middle is of a much ...
A phenocryst is an early forming, relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of an igneous rock. Such rocks that have a distinct difference in the size of the crystals are called porphyries, and the adjective porphyritic is used to describe them.
In hand specimen, many of the hornblende and biotite dacites are grey or pale brown and yellow rocks with white feldspars, and black crystals of biotite and hornblende. Other dacites, especially pyroxene-bearing dacites, are darker colored. [4] In thin section, dacites may have an aphanitic to porphyritic texture.
Photomicrograph of thin section of latite (in plane polarised light) Photomicrograph of thin section of latite (in cross polarised light) Latite is an igneous, volcanic rock, with aphanitic-aphyric to aphyric-porphyritic texture. It is the volcanic equivalent of monzonite.
On the thin section and hand-sized specimen scale a metamorphic rock may manifest a planar penetrative fabric called a foliation or a cleavage. Several foliations may be present in a rock, giving rise to a crenulation. Identifying a foliation and its orientation is the first step in analysis of foliated metamorphic rocks.
Igneous textures include the rock textures occurring in igneous rocks. Igneous textures are used by geologists in determining the mode of origin of igneous rocks and are used in rock classification. The six main types of textures are phaneritic, aphanitic, porphyritic, glassy, pyroclastic, and pegmatitic.
Thin sections of soils. Collection of Prof. Kubiëna Archived 22 September 2020 at the Wayback Machine; Uncommon igneous, metamorphic and metasomatic rocks in thin section, in unpolarized light and under crossed polarizers; Namethatmineral.com: dynamic data-tables for identification of thin sections under the microscope