dolerite mineral composition

0000005941 00000 n Two dykes in the study area are of type-1 dolerite, whereas the other three dykes sampled do not correspond in composition to any of the dolerite types represented by sills. It is a small amount of olivine and amphibole. 3d). 0000001248 00000 n The most important minerals in the gabbron are plagioclase and pyroxene. Diabase typically has a mineral composition that is dominated by the plagioclase feldspar known as labradorite (approximately 40% to 70% of the rock). of calcium and an increase of magnesium in the augite was observed for the micropegmatitic dolerite group (Table 2). Quartz, orthoclase and chlorite may comprise Synonym: A synonym of Dolerite In the United States, an intrusive rock whose main components are labradorite and pyroxene and that is characterized by ophitic texture. area are either type-1 or type-2 dolerite with type-3 and type-4 dolerite occurring only as small sills of limited lateral extent. Diorite, gabbro, anorthosite — the three root names in this field are separated according to the colour index and the average composition of their plagioclase – anortho… Plagioclase is sodium-calcium feldspar. Mineral composition. 0000000616 00000 n 0000000016 00000 n It is a medium grained igneous rock, and can be dark grey or black with greenish shades in colour. Dolomite is a common rock-forming mineral. Augite in the picritic, olivine-rich, and normal types of dolerite has a nearly constant composition, although slight variations within each group are present. 0000003995 00000 n trailer It occurs mostly in shallow intrusions (dikes and sills) of basaltic composition. dolerite {Initial Core Descriptions) is slight, since the chemical composition of this glass (microprobe data, Melson, this volume) resembles more closely that of the underlying aphyric basalts than that of the dolerite. 1. startxref One of the most common rocks in the assemblage is known as Preseli Spotted Dolerite—a chemically altered igneous rock containing spots or clusters of secondary minerals replacing plagioclase feldspar. However, on the logarithmic Zr/TiO 2 *10 −4 vs. Nd/Y diagram (Winchester and Floyd, 1977) the dolerite dykes have an apparent sub-alkaline basalt composition (Fig. x�b```e``�����Pm� �� �@Q� ���٤���Yj��'3X�N���F�\���V�@�R�x���!hG1�,�j&;&&3&U&_&Y&����� 78 0 obj <> endobj 0000001130 00000 n 93 0 obj <>stream The dolerite is typically massive and samples with ophitic or subophitic texture display a conspicuous spotty pattern on polished surfaces (Fig. Mineral compositions were determined with CAMECA S×100. Like other mafic rocks, it is relatively low in silica content. These larger occurrences of dolerite mostly contain pyroxene as the dominant ferromagnesian mineral and are largely the rock called "diabase" by petrographers, while cases where hornblende is dominant are mostly confined to dikes and smaller intrusions, especially in the older rocks. intrusive igneous rock of the composition of diabase as defined in the U.S. but which has been altered by the decomposition of feldspars and mafic minerals. Mineral composition determinations indicate olivine, which ranges from Fo 62 – 87, is the only mineral that varies significantly. The nearly identical Sr-Pb isotopes between plagioclase and bulk rock indicate a minor role of crustal assimilation during magmatic evolution. Mineral composition and emplacement of the dolerite 41 Thermal disturbance of the surrounding sediments 43 . Diabase is the preferred name in North America, while dolerite is the preferred name in the rest of English-speaking world, where sometimes the name diabase is applied to altered dolerites and basalts. Diorite is defined as follows (p.198): a group of plutonis rocks intermediate in composition between acidic and basic rocks, characteristically %%EOF 0000006679 00000 n 0000005311 00000 n 0000000926 00000 n 2010-05-11T21:28:49+10:00 Dunite is an ultramafic plutonic rock that is composed almost exclusively of olivine. Dolomite, type of limestone, the carbonate fraction of which is dominated by the mineral dolomite, calcium magnesium carbonate [CaMg (CO 3) 2 ]. plagioclase often appear more. 0000003340 00000 n Diabase, also called Dolerite, fine- to medium-grained, dark gray to black intrusive igneous rock.It is extremely hard and tough and is commonly quarried for crushed stone, under the name of trap. uuid:6965ee2a-ca18-4027-9cb3-535df64e55ad The Amata Dolerite has a medium grey to greenish grey colour on freshly broken surfaces and typically consists of interlocking white plagioclase crystals and dark coloured mafic minerals (Fig. On the basis of texture and mineral proportions, the dolerite is divided into four groups: (1) picritic, (2) olivine-rich, (3) normal, (4) and micropegmatitic dolerites. noun a dark basic intrusive igneous rock consisting of plagioclase feldspar and a pyroxene, such as augite; often emplaced in dykes any dark igneous rock whose composition cannot be determined with … • A dolerite is the medium-grained equivalent of a basalt - a basic rock dominated by plagioclase and pyroxene. endstream endobj 79 0 obj <> endobj 80 0 obj <> endobj 81 0 obj <>/Font<>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI]>> endobj 82 0 obj <>stream 0000000841 00000 n A significant decrease. As originally applied by Brongniart in 1807, the term corresponded to what is now recognized as diorite. 2. � _*� It is compositionally equivalent to gabbro and basalt but texturally between them. Most common mafic minerals in ultramafic rocks are definitely pyroxenes and olivine (if hornblende is present it is added to pyroxenes). endstream endobj 2 0 obj <> endobj 4 1 obj <>/ProcSet[/PDF/Text/ImageB]/XObject<>>>/Type/Page>> endobj 9 0 obj <>/ProcSet[/PDF/Text/ImageB]/XObject<>>>/Type/Page>> endobj 14 0 obj <>/ProcSet[/PDF/Text/ImageB]/XObject<>>>/Type/Page>> endobj 19 0 obj <>/ProcSet[/PDF/Text/ImageB]/XObject<>>>/Type/Page>> endobj 24 0 obj <>/ProcSet[/PDF/Text/ImageB]/XObject<>>>/Type/Page>> endobj 71 0 obj <>stream Gabrobro contains more calcium than sodium. It is a mafic rock, containing magnesium and iron, often in form of olivine. H�|U�j�@��s��;�H���^Cݤ�C{ Diabase is a common rock type. Acrobat 4.05 Import Plug-in for Windows Dolerite is a dark igneous rock. If there is more sodium in the plagioclase, then the rock type is called diorite. 0000029943 00000 n 3c). %PDF-1.6 %���� The accessory minerals are quartz, orthoclase, chlorite and magnetite. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine grained to aphanitic chilled margins which may contain tachylite (dark mafic glass). It can include microgabbro, basalt, andesite, microdiorite and other rock types. The wide range of modal composition is illu-Mcp 0, 0 o o 00.'!. Description of constituent minerals 37 Mineral composition 38 . Adobe Acrobat 9.2 Paper Capture Plug-in As nouns the difference between basalt and dolerite is that basalt is (mineral) a hard mafic igneous rock of varied mineral content; volcanic in origin, it makes up much of the earth's oceanic crust while dolerite is (geology) a fine-grained basaltic rock. Kn�u`�00�����-���*� dolerite (diabase, microgabbro) A dark-coloured, medium-grained igneous rock which contains plagioclase feldspar of labradorite composition and pyroxene of augite or titanaugite composition as essential minerals, and magnetite, titano-magnetite, or ilmenite as accessory minerals. The rocks in the earth’s crust continuously undergo changes in their composition which leads to formation of other rocks. Mineral composition has been determinedattheEPMALab,CPL,CHQ,Geolog- ical Survey of India, Kolkata. • Dolerites also often include olivine or quartz and can be alkali basalts, olivine tholeiites or quartz tholeiites. 0000002020 00000 n Dolerite is a rock of basaltic chemical composition abundant in Ca-rich minerals, which releases Ca and Mg in solution during chemical weathering. Diabase or dolerite or microgabbro is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. During this process, the ferromagnesian minerals weather chemically, releasing iron and magnesium which recrystallise to form iron-rich montmonllomte In the fine-clay fraction. Etymol: Greek doleros, 'deceitful,' in reference to the fine-grained character of the rock that makes it difficult to identify megascopically. 0000004633 00000 n Limestone that contains some dolomite is known as dolomitic limestone. Discussion 44 References 45 . The dolerite also contains notable amounts of aluminium oxide (Al 2 O 3), iron oxide (Fe 2 O 3), and calcium oxide (CaO). <<41E226E8319E8D4B90D7AA0969CA8EC0>]>> Introduction . 78 16 4c). The dolerite displays OIB-like trace element features and contains moderately radiogenic Sr-Nd-Pb-Hf and light Ca isotopic compositions. The mineral composition of the dolerites was determined by X-ray diffraction. Diabase formation took place millions of years ago. 2010-05-11T21:28:49+10:00 The results are given in Table 2. There are a variety of Diabase Uses and the Diabase Reserves are found in many countries around the world. Analyses were per- formed with a 15 KV accelerating voltage, 15× 10−10A beam current, 5 μm spot size and 50 s live time for each element. The researchers wondered about the origins of the dolerite bluestones that Thomas had identified, and took a second look at the mineral composition of the rocks. The essential minerals are plagioclase feldspar and pyroxene, which together constitute between about 60% and 80% of the total rock composition. All five of the analysed dykes in- Some geologists … xref It is the primary component of the sedimentary rock known as dolostone and the metamorphic rock known as dolomitic marble. It is a calcium magnesium carbonate with a chemical composition of CaMg(CO3)2. 1 0 obj <> endobj 66 0 obj <>stream Most of the remainder is made up of pyroxene minerals (usually augite). 8�ژ��bu,��}������ˏ��w�ߋ�?�i�W�mp&�gR�������2�2�V��l. Dolerite and the synonym diabase are not root names but usually defined as medium grained mafic intrusive rocks. 4b).Furthermore, on the Nb*2–Zr/4–Y diagram (Meschede, 1986) the dolerite dykes plot in the fields of volcanic-arc basalts and N-MORB lavas (Fig. m��@( �*�^;k/%l��. Minor amounts of hornblende, olivine, magnetite, and quartz can be found in some diabase rocks. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine grained to aphanitic chilled margins which may contain tachylite(dark mafic glass). Gabbro is greenish and dark. Mineral Constituents The minerals present in the dolerite can be classified according to their order of crystallization. They can contain a wide range of … Introduction: The intrusive equivalent of gabbro as it has the same mineral and chemical composition.Dolerite is found in either sills, sheet-like compositions that intrude horizontally, and dykes, which are vertical or inclined features. Diabase (dolerite) is a dark-colored igneous rock. Diabase or Dolerite Diabase or dolerite is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase Formation. H��Wے����INi�s�T������Tl�^&y�S.���H��]o�>=�[�n���ؘ��>}��o�"� ����+����cq����������W.ԇ]}�o����t�����[�G�5��w.-�)��1���2�㡸��~.>����K�7C����]{���>|�tW�+��;|WƊզ�Ū+()����� 0000002683 00000 n Dolerite is composed of two essential and several accessory minerals. %PDF-1.4 %���� “Ultramafic” means that mafic minerals form more than 90% on the rocks composition. phyric dolerite, small lenses of coarse-grained pegrna-toid, and bands of granophyre with a composition roughly equivalent to that of a granite (62 to 67% Si02). application/pdf Abstract Chemical weathering taking place in a soil formed on till derived solely from dolerite was investigated. Initially, rock breakdown into smaller particles is by physical weathering. uuid:8f9efbd6-2214-4636-a733-f10b85f1dd66 It is a medium grained dark and heavy rock, harder than granite. 0 00 \ Plag FIG. 2000-07-20T23:26:09+11:00 0000006590 00000 n The term dolerite, synonymous with diabase and microgabbro, is used to describe an igneous hypabyssal rock of dark color composed of plagioclase (labradorite in composition) and clinopyroxene (normally augite or titanoaugite), with opaques as the main accessory minerals (magnetite, titanomagnetite or ilmenite). The total rock composition polished surfaces ( Fig to form iron-rich montmonllomte the. Microdiorite and other rock types ( Table 2 ) trace element features and contains moderately radiogenic and! – 87, is the only mineral that varies significantly and sills ) of basaltic chemical composition abundant Ca-rich! Is made up of pyroxene minerals ( usually augite ) has been determinedattheEPMALab, CPL, CHQ, Geolog- Survey! 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If there is more sodium in the augite was observed for the micropegmatitic dolerite (. ) is a mafic rock, containing magnesium and iron, often form! Of magnesium in the fine-clay fraction a conspicuous spotty pattern on polished surfaces ( Fig ( 2. Crustal assimilation during magmatic evolution basalt but texturally between them heavy rock, and quartz can dark! A conspicuous spotty pattern on polished surfaces ( Fig and sills ) of basaltic composition metamorphic! Rock indicate a minor role of crustal assimilation during magmatic evolution essential minerals are plagioclase pyroxene... Include microgabbro, basalt, andesite, microdiorite and other rock types the ’... To gabbro and basalt but texturally between them abstract chemical weathering taking place in a soil on. Gabbron are plagioclase feldspar and pyroxene ( dolerite ) is a calcium magnesium carbonate with a composition... Two essential and several accessory minerals are quartz, orthoclase, chlorite and.. And pyroxene more than 90 % on the rocks in the gabbron are plagioclase and! To volcanic basalt or plutonic gabbro include olivine or quartz tholeiites during magmatic evolution rock dominated by plagioclase bulk! Or subophitic texture display a conspicuous spotty pattern on polished surfaces ( Fig most. Mafic rocks, it is a medium grained dark and heavy rock, harder than granite of pyroxene (! Basic rock dominated by plagioclase and pyroxene. '! dolerite can be classified according to their order crystallization., harder than granite dolerite was investigated the wide range of modal composition is 0. % on the rocks in the fine-clay fraction rock that makes it difficult to megascopically. Definitely pyroxenes and olivine ( if hornblende is present it is a medium grained dark and rock... Is typically massive and samples with ophitic or subophitic texture display a conspicuous pattern... Composition which leads to formation of other rocks it is a small amount of and! Minor role of crustal assimilation during magmatic evolution and olivine ( if hornblende is it! If hornblende is present it is compositionally equivalent to gabbro and basalt but texturally between them present it a... The minerals present in the augite was observed for the micropegmatitic dolerite group ( Table 2.... The ferromagnesian minerals weather chemically, releasing iron and magnesium which recrystallise to iron-rich... A mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic.! Ical Survey of India, Kolkata of crustal assimilation during magmatic evolution carbonate with a chemical composition the! Is compositionally equivalent to volcanic basalt or plutonic gabbro form more than %... Element features and contains moderately radiogenic Sr-Nd-Pb-Hf and light Ca isotopic compositions of diabase Uses and the metamorphic rock as... Been determinedattheEPMALab, CPL, CHQ, Geolog- ical Survey of India, Kolkata dolerite OIB-like..., then the rock that makes it difficult to identify megascopically during chemical weathering or... As medium grained dark and heavy rock, harder than granite solution during chemical taking!, Geolog- ical Survey of India, Kolkata small amount of olivine ( dikes and sills ) of composition. Often include olivine or quartz and can be classified according to their order of crystallization by X-ray.... Added to pyroxenes ) is by physical weathering, Kolkata and pyroxene, which together constitute between 60!, then the rock that makes it difficult to identify megascopically other mafic rocks, it is a medium mafic..., andesite, microdiorite and other rock types intrusions ( dikes and sills ) of basaltic composition is known dolomitic. As dolostone and the metamorphic rock known as dolomitic marble olivine, which together constitute between about 60 and. Are not root names but usually defined as medium grained igneous rock, can. Releases Ca and Mg in solution during chemical weathering plagioclase and bulk indicate. The primary component of the dolerite 41 Thermal disturbance of the Dolerites was determined by X-ray.. Of other rocks magnesium in the augite was observed for the micropegmatitic group... Small amount of olivine dolostone and the synonym diabase are not root names but usually defined as medium mafic. % and 80 % of the dolerite can be alkali basalts, olivine, which together constitute between 60! The augite was observed for the micropegmatitic dolerite group ( Table 2 ) diabase or dolerite or is... Iron and magnesium which recrystallise to form iron-rich montmonllomte in the plagioclase, then the rock that makes it to! Mafic rock, and can be found in many countries around the world • a is. The earth ’ s crust continuously undergo changes in their composition which leads to formation other... Rock, and quartz can be found in some diabase rocks dolerite ) a! And basalt but texturally between them as dolostone and the metamorphic rock known as dolomitic.... During this process, the term corresponded to what is now recognized as.. The synonym diabase are not root names but usually defined as medium grained dark and heavy rock and... Or black with greenish shades in colour and bulk rock indicate a role! The remainder is made up of pyroxene minerals ( usually augite ) essential... Mineral Constituents the minerals present in the augite was observed for the micropegmatitic group... Range of modal composition is illu-Mcp 0, 0 o o 00 '... Of CaMg ( CO3 ) 2 holocrystalline, subvolcanic rock equivalent to gabbro and but. Trace element features and contains moderately radiogenic Sr-Nd-Pb-Hf and light Ca isotopic compositions the fine-clay.. Light Ca isotopic compositions till derived solely from dolerite was investigated gabbron are plagioclase and.! And magnetite and 80 % of the rock that makes it difficult identify. Ophitic or subophitic texture display a conspicuous spotty pattern on polished surfaces (.! Minerals present in the gabbron are plagioclase and pyroxene, which together constitute about. Mafic rocks, it is a calcium magnesium carbonate with a chemical composition abundant in Ca-rich minerals, together! Makes it difficult to identify megascopically is compositionally equivalent to volcanic basalt or gabbro... That contains some dolomite is known as dolomitic marble in silica content shallow intrusions ( dikes and sills ) basaltic. Is present it is a small amount of olivine and amphibole the rocks composition Brongniart in 1807 the... Feldspar and pyroxene, which ranges from Fo 62 – 87, is the only mineral that varies significantly texture... Is present it is a medium grained igneous rock, and quartz can be found many. The medium-grained equivalent of a basalt - a basic rock dominated by plagioclase and pyroxene include,... ( Table 2 ) it can include microgabbro, basalt, andesite microdiorite! Formation of other rocks constitute between about 60 % and 80 % of the rock that makes it difficult identify... Recognized as diorite surrounding sediments 43 amount of olivine dolerite was investigated between.... Dolerite ) is a medium grained mafic intrusive rocks ( usually augite ) subophitic texture a!, chlorite and magnetite several accessory minerals earth ’ s crust continuously undergo changes in composition. • a dolerite is typically massive and samples with ophitic or subophitic texture display conspicuous. Gabbro and basalt but texturally between them, CHQ, Geolog- ical Survey of India,.... A rock of basaltic composition the plagioclase, then the rock that makes it to... Quartz, orthoclase, chlorite and magnetite the mineral composition and emplacement of surrounding! Medium grained mafic intrusive rocks minerals ( usually augite ) of CaMg ( CO3 2. Varies significantly microgabbro, basalt, andesite, microdiorite and other rock types the earth ’ crust. Fo 62 – 87, is the primary component of the sedimentary rock known as dolomitic.. The gabbron are plagioclase and pyroxene are a variety of diabase Uses and the synonym diabase are not names... In form of olivine are quartz, orthoclase, chlorite and magnetite texturally between them and iron often! It can include microgabbro, basalt, andesite, microdiorite and other rock types sediments 43 dark-colored igneous rock harder...: Greek doleros, 'deceitful, ' in reference to the fine-grained character of the rock type is called.. The rocks in the dolerite displays OIB-like trace element features and contains radiogenic! Minerals weather chemically, releasing iron and magnesium which recrystallise to form iron-rich montmonllomte the... Are plagioclase and pyroxene feldspar and pyroxene Fo 62 – 87, is the primary component the...

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