|
Theralite
Theralite (from Greek "to pursue") is, in petrology, the name given to calcic foidal gabbro, a plutonic hylocrystalline rock consisting of augite, olivine, calcic plagioclase (labradorite), and nepheline, along with accessories including biotite, magnetite, ilmenite and analcime. Theralite is the intrusive equivalent of nepheline basanite, a foidal basalt with essential calic plagioclase and essential olivine. Tephrite is foidal basalt with essential calic plagioclase but without essential olivine. It is essentially the volcanic equivalent of essexite. The discovery of theralite was looked forward to with interest as it was of rare occurrence, and as completing the series of basic rocks containing nepheline as an essential constituent. With the increase in silica (SiO2) and the concomitant reduction in nepheline, theralite becomes gabbro. With a decrease in silica and reduction in olivine theralite grades into teschenite and with the addition of sodic feldspar, grades into es ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Petrology
Petrology () is the branch of geology that studies rocks and the conditions under which they form. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. Igneous and metamorphic petrology are commonly taught together because they both contain heavy use of chemistry, chemical methods, and phase diagrams. Sedimentary petrology is, on the other hand, commonly taught together with stratigraphy because it deals with the processes that form sedimentary rock. Background Lithology was once approximately synonymous with petrography, but in current usage, lithology focuses on macroscopic hand-sample or outcrop-scale description of rocks while petrography is the speciality that deals with microscopic details. In the petroleum industry, lithology, or more specifically mud logging, is the graphic representation of geological formations being drilled through and drawn on a log called a mud log. As the cuttings are circulated out of the borehole, they are sample ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basanite
Basanite () is an igneous, volcanic (extrusive) rock with aphanitic to porphyritic texture. It is composed mostly of feldspathoids, pyroxenes, olivine, and plagioclase and forms from magma low in silica and enriched in alkali metal oxides that solidifies rapidly close to the Earth's surface. Description Basanite is an aphanitic (fine-grained) igneous rock that is low in silica and enriched in alkali metals. Of its total content of quartz, feldspar, and feldspathoid ( QAPF), between 10% and 60% by volume is feldspathoid and over 90% of the feldspar is plagioclase. Quartz is never present. This places basanite in the basanite/tephrite field of the QAPF diagram. Basanite is further distinguished from tephrite by having a normative olivine content greater than 10%. While the IUGS recommends classification by mineral content whenever possible, volcanic rock can be glassy or so fine-grained that this is impractical, and then the rock is classified chemically using the TAS classifica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monzonite
Monzonite is an igneous intrusive rock, formed by slow cooling of underground magma that has a moderate silica content and is enriched in alkali metal oxides. Monzonite is composed mostly of plagioclase and alkali feldspar. Syenodiorite is an obsolescent term for monzonite or for monzodiorite.Le Maitre, R.W., ''Igneous Rocks: A Classification and Glossary of Terms'' Cambridge University Press, 2nd ed, pp. 113 Larvikite is a particular form of monzonite. Description Monzonite is a coarse-grained (phaneritic) igneous rock. Such rocks are classified by their relative percentages of quartz, plagioclase, alkali feldspar, and feldspathoid (the QAPF classification). Monzonite is defined as rock having less than 5% quartz in its QAPF fraction and in which alkali feldspar makes up between 35% and 65% of the total feldspar content. If quartz constitutes greater than 5% of the QAPF fraction, the rock is termed a quartz monzonite, while if feldspathoids are present as up to 10% of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Essexite
Essexite (), also called nepheline monzogabbro (), is a dark gray or black holocrystalline plutonic igneous rock. Its name is derived from the type locality in Essex County, Massachusetts, in the United States. Modern petrology identifies rocks according to mineralogical criteria. Utilising the IUGS QAPF diagram of Streckeisen (1974) "essexite" is more formally known as nepheline monzodiorite or nepheline monzogabbro depending on the ratio of orthoclase to plagioclase and the abundance of nepheline. Petrology In order to produce a magma composition suitable for forming essexite the partial melting of the source rocks must be restricted, generally to less than 10% partial melting. This favors producing a melt rich in large-ion lithophile elements (LILE) such as K, Ba, Rb, Cs, Sr. The source melts of essexites contain more aluminium and alkali ions than available silica tetrahedra, which is why essexites crystallise nepheline instead of plagioclase. Higher than normal p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in sea water, aqua regia, and chlorine. Titanium was discovered in Cornwall, Great Britain, by William Gregor in 1791 and was named by Martin Heinrich Klaproth after the Titans of Greek mythology. The element occurs within a number of minerals, principally rutile and ilmenite, which are widely distributed in the Earth's crust and lithosphere; it is found in almost all living things, as well as bodies of water, rocks, and soils. The metal is extracted from its principal mineral ores by the Kroll and Hunter processes. The most common compound, titanium dioxide, is a popular photocatalyst and is used in the manufacture of white pigments. Other compounds include titanium tetrachloride (TiCl4), a component of smoke screens and catalysts; and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyroxene
The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) or magnesium (Mg) and more rarely zinc, manganese or lithium, and Y represents ions of smaller size, such as chromium (Cr), aluminium (Al), magnesium (Mg), cobalt (Co), manganese (Mn), scandium (Sc), titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ... (Ti), vanadium (V) or even iron (Fe II) or (Fe III). Although aluminium substitutes extensively for silicon in silicates such as feldspars and amphiboles, the substitution occurs only to a limited extent in most pyroxenes. They share a common structure consisting of single chains of si ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shonkinite
Shonkinite is an intrusive igneous rock found in few places in the world. It is unique in having low silica, feldspathoid minerals, and large blocky crystals of black augite. It makes up much of the hard dark grey rock comprising certain mountains and buttes in Montana that are remnants of laccoliths and stocks, such as the Highwood mountains. Composition Shonkinite is an intrusive igneous rock. More specifically, it is a mafic foidal (feldspathoid bearing) syenite, a holocrystalline (completely crystalline) intrusive rock which, , is composed of potassic feldspar in the form of sanidine, nepheline, augite, biotite, and olivine. Shonkinite is also used for mafic nepheline syenite with aegerine-augite as the pyroxene, and with the addition of plagioclase (andesine to labradorite). Nepheline in shonkinite from the is largely altered to natrolite and stilbite. The close view of the rocks in the Adel mountains show large glossy crystals of augite in a dark grey matrix made up of s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Essexite
Essexite (), also called nepheline monzogabbro (), is a dark gray or black holocrystalline plutonic igneous rock. Its name is derived from the type locality in Essex County, Massachusetts, in the United States. Modern petrology identifies rocks according to mineralogical criteria. Utilising the IUGS QAPF diagram of Streckeisen (1974) "essexite" is more formally known as nepheline monzodiorite or nepheline monzogabbro depending on the ratio of orthoclase to plagioclase and the abundance of nepheline. Petrology In order to produce a magma composition suitable for forming essexite the partial melting of the source rocks must be restricted, generally to less than 10% partial melting. This favors producing a melt rich in large-ion lithophile elements (LILE) such as K, Ba, Rb, Cs, Sr. The source melts of essexites contain more aluminium and alkali ions than available silica tetrahedra, which is why essexites crystallise nepheline instead of plagioclase. Higher than normal p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tephrite
Tephrite is an igneous, volcanic (extrusive) rock, with aphanitic to porphyritic texture. Mineral content is usually abundant feldspathoids (leucite or nepheline), plagioclase, and lesser alkali feldspar. Pyroxenes (clinopyroxenes) are common accessory minerals. Quartz and olivine are absent. Occurrences include leucite nepheline tephrite from Hamberg bei Neckarelz near Heidelberg, Germany,Frenzel, Gerhard (1953) ''Die Erzparagenese des Katzenbuckels im Odenwald'', Contributions to Mineralogy and Petrology, Volume 3, Number 6, pages 409-444, DOI: 10.1007/BF01129196 . Retrieved 2012-04-11. phonolite-tephrite at Monte Vulture, Basilicata, Italy and basanite–tephrite intrusions in Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea .... References Volcanic rocks {{Petr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial planet, rocky planet or natural satellite, moon. More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt is chemically equivalent to slow-cooling, coarse-grained gabbro. The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is also an important rock type on other planetary bodies in the Solar System. For example, the bulk of the plains of volcanism on Venus, Venus, which cover ~80% of the surface, are basaltic; the lunar mare, lunar maria are plains of flood-basaltic lava flows; and basalt is a common rock on the surface of Mars. Molten basalt lava has a low viscosity due to its relatively low silica content (between 45% and 52%), resulting in rapidly moving lava flo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Analcime
Analcime (; ) or analcite is a white, gray, or colorless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is Na Al Si2 O6· H2O. Minor amounts of potassium and calcium substitute for sodium. A silver-bearing synthetic variety also exists (Ag-analcite). Analcime is usually classified as a zeolite mineral, but structurally and chemically it is more similar to the feldspathoids. Analcime occurs as a primary mineral in analcime basalt and other alkaline igneous rocks. It also occurs as cavity and vesicle fillings associated with prehnite, calcite, and zeolites. Locations Well known locations for sourcing analcime include Croft Quarry in Leicestershire, UK; the Cyclopean Islands east off Sicily and near Trentino in northern Italy; Victoria in Australia; Kerguelen Island in the Indian Ocean; in the Lake Superior copper district of Michigan, Bergen Hill, New Jersey, Golden, Colorado, and at Searles Lake, C ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feldspathoid
The feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content. They occur in rare and unusual types of igneous rocks, and are usually not found in rocks containing primary quartz. A notable exception where feldspathoids and quartz-bearing rocks are found together is the Red Hill Syenite. Foid, a contraction of the term ''feldspathoid'', is applied to any igneous rock containing up to 60% modal feldspathoid minerals. For example, a syenite with significant nepheline Nepheline, also called nephelite (), is a rock-forming mineral in the feldspathoid groupa silica-undersaturated aluminosilicate, Na3 K Al4 Si4 O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatite ... present can be termed a ''nepheline-bearing syenite'' or ''nepheline syenite'', with the term ''nepheline'' replaceable by any foid mineral. Such terminology is used in the Streckeisen ( QAPF ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
