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In geology, country rock is the rock native to an area, in contrast to any intrusion of viscous geologic material, commonly magma, or perhaps rock salt (in salt domes) or unconsolidated sediments. [1] A dike (dark) intrudes into the country rock (light), Baranof Island, Alaska, United States
A xenolith ("foreign rock") is a rock fragment (country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock entrained during magma ascent, emplacement and eruption. [1]
Rock outcrop along a mountain creek near Orosí, Costa Rica. Rocks are classified according to characteristics such as mineral and chemical composition, permeability, texture of the constituent particles, and particle size. These physical properties are the result of the processes that formed the rocks. [5]
The Lower Reef is composed of norites and feldspathic pyroxenites that have been recrystallized and overprinted. This layer has abundant country-rock xenoliths particularly near the base of the layer. The Central or Middle Reef is composed of igneous peridotite and recrystallized "vari-textured" mafic rocks with metasedimentary xenoliths.
The metamorphism of greenstones has generally led to the formation of hornblende-plagioclase rocks. [31] A feature of the granites of the batholith is the high concentrations of volatile components. Fluids rich in these have strongly affected the country rock and locally the granites themselves in a process called metasomatism.
The result is a distinct boundary of very fine grain igneous rock along the border of the country rock. [3] The surrounding rock may be "baked" through contact metamorphism, resulting in non-foliated metamorphic rocks. [1] Rocks that were originally limestone, quartz sandstone, and shale become marble, quartzite, and hornfels, respectively.
The geology of England is mainly sedimentary. The youngest rocks are in the south east around London , progressing in age in a north westerly direction. [ 1 ] The Tees–Exe line marks the division between younger, softer and low-lying rocks in the south east and the generally older and harder rocks of the north and west which give rise to ...
Steeply-tilted layers of flysch on the coast of Bay of Biscay, at Zumaia, Basque Country, Spain. Flysch (/ f l ɪ ʃ /) is a sequence of sedimentary rock layers that progress from deep-water and turbidity flow deposits to shallow-water shales and sandstones. It is deposited when a deep basin forms rapidly on the continental side of a mountain ...