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USGS scientist examines pumice blocks at the edge of a pyroclastic flow from Mount St. Helens Rocks from the Bishop Tuff, uncompressed with pumice on left; compressed with fiamme on right. Flight through a μCT-image stack of a lapillus of the volcano Katla in Iceland. Find spot: Beach near Vik at the end of road 215. Acquisition done using "CT ...
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 ...
Moving forward and backward on the X-axis. (Surge) Moving left and right on the Y-axis. (Sway) Moving up and down on the Z-axis. (Heave) Rotational envelopes: Tilting side to side on the X-axis. Tilting forward and backward on the Y-axis. Turning left and right on the Z-axis.
In geology, texture or rock microstructure [1] refers to the relationship between the materials of which a rock is composed. [2] The broadest textural classes are crystalline (in which the components are intergrown and interlocking crystals), fragmental (in which there is an accumulation of fragments by some physical process), aphanitic (in which crystals are not visible to the unaided eye ...
(Left) Randomly-orientated grains in a rock before metamorphism. (Right) Grains align orthogonal to the applied stress if a rock is subjected to stress during metamorphism. Metamorphism is the set of processes by which existing rock is transformed physically or chemically at elevated temperature, without actually melting to any great degree.
Volcaniclastics are composed of a range of pyroclastic detritus mixed with epiclastic sediments and formed in variable depositional environments. [7] [8] Volcaniclastics include pyroclastic rock and tephra; volcanic autoclastic, alloclastic, and epiclastic materials; and fault gouge where faults displace volcanic rock. [2] All are defined below.
Andesite is an aphanitic (fine-grained) to porphyritic (coarse-grained) igneous rock that is intermediate in its content of silica and low in alkali metals. It has less than 20% quartz and 10% feldspathoid by volume, with at least 65% of the feldspar in the rock consisting of plagioclase .
"Imperial Porphyry" from the Red Sea Mountains of Egypt A waterworn cobble of porphyry Rhyolite porphyry from Colorado; scale bar in lower left is 1 cm (0.39 in). Porphyry (/ ˈ p ɔːr f ə r i / POR-fə-ree) is any of various granites or igneous rocks with coarse-grained crystals such as feldspar or quartz dispersed in a fine-grained silicate-rich, generally aphanitic matrix or groundmass.