|
Trachyte
Trachyte () is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanite, aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava (or shallow intrusions) enriched with silica and alkali metals. It is the volcanic equivalent of syenite. Trachyte is common wherever alkali magma is erupted, including in late stages of ocean island volcanismMacDonald 1983, pp. 51–52 and in continental rift valleys, above mantle plumes,Philpotts and Ague 2009, pp. 390–394 and in areas of back-arc extension. Trachyte has also been found in Gale crater on Mars. Trachyte has been used as decorative building stone and was extensively used as dimension stone in the Roman Empire and the Republic of Venice. Chemical composition Trachyte has a silica content of 60 to 65% and an alkali oxide content of over 7%. This gives it less SiO2 than rhyolite and more (Na2O plus K2O) than dacite. These chemical differe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhyolite
Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matrix (geology), groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent of granite. Its high silica content makes rhyolitic magma extremely viscosity, viscous. This favors explosive eruptions over effusive eruptions, so this type of magma is more often erupted as pyroclastic rock than as lava flows. Rhyolitic ash-flow tuffs are among the most voluminous of continental igneous rock formations. Rhyolitic tuff has been used extensively for construction. Obsidian, which is rhyolitic volcanic glass, has been used for tools from prehistoric times to the present day because it can be shaped to an extremely sharp edge. Rhyolitic pumice finds use as an abrasive, in concrete, and as a soil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dacite
Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. It is composed predominantly of plagioclase feldspar and quartz. Dacite is relatively common, occurring in many tectonic settings. It is associated with andesite and rhyolite as part of the subalkaline tholeiitic and calc-alkaline magma series. Etymology The word ''dacite'' comes from Dacia, a province of the Roman Empire which lay between the Danube River and Carpathian Mountains (now modern Romania and Moldova) where the rock was first described. The term ''dacite'' was used for the first time in the scientific literature in the book ''Geologie Siebenbürgens'' (''The Geology of Transylvania'') by Austrian geologists Franz Ritter von Hauer and Guido Stache. Dacite was originally defined as a new rock type to separate calc-alkaline ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sanidine
Sanidine is the high temperature form of potassium feldspar with a general formula K(AlSi3O8). Sanidine is found most typically in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal system. Orthoclase is a monoclinic polymorph stable at lower temperatures. At yet lower temperatures, microcline, a triclinic polymorph of potassium feldspar, is stable. Due to the high temperature and rapid quenching, sanidine can contain more sodium in its structure than the two polymorphs that equilibrated at lower temperatures. Sanidine and high albite constitute a solid solution series with intermediate compositions termed anorthoclase. Exsolution of an albite phase does occur; resulting cryptoperthite can best be observed in electron microprobe images. Occurrence In addition to its presence in the groundmass of felsic rocks, sanidine is a common phenocryst in rhyolites and, to a lesser extent, rhyodacites. Trachyte consists la ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Igneous Rock
Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial melts of existing rocks in either a planet's mantle or crust. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, or without crystallization to form natural glasses. Igneous rocks occur in a wide range of geological settings: shields, platforms, orogens, basins, large igneous provinces, extended crust and oceanic crust. Geological significance Igneous and metamorphic rocks make up 90–95% of the top of the Earth's crust by volume. Igneous rock ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Syenite
Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (< 5%). It is considered a granitoid. Some syenites contain larger proportions of components and smaller amounts of material than most granites; those are classed as being of . The |
Roman Empire
The Roman Empire ruled the Mediterranean and much of Europe, Western Asia and North Africa. The Roman people, Romans conquered most of this during the Roman Republic, Republic, and it was ruled by emperors following Octavian's assumption of effective sole rule in 27 BC. The Western Roman Empire, western empire collapsed in 476 AD, but the Byzantine Empire, eastern empire lasted until the fall of Constantinople in 1453. By 100 BC, the city of Rome had expanded its rule from the Italian peninsula to most of the Mediterranean Sea, Mediterranean and beyond. However, it was severely destabilised by List of Roman civil wars and revolts, civil wars and political conflicts, which culminated in the Wars of Augustus, victory of Octavian over Mark Antony and Cleopatra at the Battle of Actium in 31 BC, and the subsequent conquest of the Ptolemaic Kingdom in Egypt. In 27 BC, the Roman Senate granted Octavian overarching military power () and the new title of ''Augustus (title), Augustus'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Republic Of Venice
The Republic of Venice, officially the Most Serene Republic of Venice and traditionally known as La Serenissima, was a sovereign state and Maritime republics, maritime republic with its capital in Venice. Founded, according to tradition, in 697 by Paolo Lucio Anafesto, over the course of its History of the Republic of Venice, 1,100 years of history it established itself as one of the major European commercial and naval powers. Initially extended in the ''Dogado'' area (a territory currently comparable to the Metropolitan City of Venice), during its history it annexed a large part of Northeast Italy, Istria, Dalmatia, the coasts of present-day Montenegro and Albania as well as numerous islands in the Adriatic Sea, Adriatic and eastern Ionian Sea, Ionian seas. At the height of its expansion, between the 13th and 16th centuries, it also governed Crete, Cyprus, the Peloponnese, a number of List of islands of Greece, Greek islands, as well as several cities and ports in the eastern Me ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phenocryst
image:montblanc granite phenocrysts.JPG, 300px, Granites often have large feldspar, feldspathic phenocrysts. This granite, from the Switzerland, Swiss side of the Mont Blanc massif, has large white phenocrysts of plagioclase (that have trapezoid shapes when cut through). 1 euro coin (diameter 2.3 cm) for scale. A phenocryst is an early forming, relatively large and usually conspicuous crystal distinctly larger than the grains of the rock Matrix (geology), groundmass of an igneous rock. Such rocks that have a distinct difference in the size of the crystals are called Porphyry (geology), porphyries, and the adjective porphyritic is used to describe them. Phenocrysts often have euhedral forms, either due to early growth within a magma, or by post-emplacement recrystallization (geology), recrystallization. Normally the term ''phenocryst'' is not used unless the crystals are directly observable, which is sometimes stated as greater than in diameter. Phenocrysts below this level, but s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TAS Classification
TAS stands for Total Alkali Silica. The TAS classification can be used to assign names to many common types of volcanic rocks based upon the relationships between the combined alkali and silica contents. These chemical parameters are useful because the relative proportions of alkalis and silica are important in determining both normative mineralogy and actual mineralogy. The classification can be simple to use for rocks that have been chemically analyzed. Except for the following quotation from Johannsen (1937), this discussion is based upon Le Maitre et al (2002). Use of the TAS classification Before using the TAS or any other classification, some particular guidance by Johannsen (1937) should be kept in mind. :''Many and peculiar are the classifications that have been proposed for igneous rocks. Their variability depends in part upon the purpose for which each was intended, and in part upon the difficulties arising from the characters of the rocks themselves. The trouble is not w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dimension Stone
Dimension stone is natural stone or Rock (geology), rock that has been selected and finished (e.g., trimmed, cut, drilled or ground) to specific sizes or shapes. Color, Texture (geology), texture and pattern, and surface finish of the stone are also normal requirements. Another important selection criterion is durability: the time measure of the ability of dimension stone to endure and to maintain its essential and distinctive characteristics of strength, resistance to decay, and appearance. quarry, Quarries that produce dimension stone or crushed stone (used as construction aggregate) are interconvertible. Since most quarries can produce either one, a crushed stone quarry can be converted to dimension stone production. However, first the stone shattered by heavy and indiscriminate blasting must be removed. Dimension stone is separated by more precise and delicate techniques, such as diamond wire saws, diamond belt saws, burners (jet-piercers), or light and selective blasting wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
