dolerite mineral composition

Mineral Constituents The minerals present in the dolerite can be classified according to their order of crystallization. Kn�u`�00�����-���*� Mineral composition has been determinedattheEPMALab,CPL,CHQ,Geolog- ical Survey of India, Kolkata. 0000003340 00000 n The wide range of modal composition is illu-Mcp 0, 0 o o 00.'!. Augite in the picritic, olivine-rich, and normal types of dolerite has a nearly constant composition, although slight variations within each group are present. H�|U�j�@��s��;�H���^Cݤ�C{ It occurs mostly in shallow intrusions (dikes and sills) of basaltic composition. 0000002020 00000 n There are a variety of Diabase Uses and the Diabase Reserves are found in many countries around the world. Dolerite is composed of two essential and several accessory minerals. of calcium and an increase of magnesium in the augite was observed for the micropegmatitic dolerite group (Table 2). It is the primary component of the sedimentary rock known as dolostone and the metamorphic rock known as dolomitic marble. Introduction . %%EOF It is a medium grained igneous rock, and can be dark grey or black with greenish shades in colour. A significant decrease. The nearly identical Sr-Pb isotopes between plagioclase and bulk rock indicate a minor role of crustal assimilation during magmatic evolution. 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. 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 0000006590 00000 n Minor amounts of hornblende, olivine, magnetite, and quartz can be found in some diabase rocks. 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. 0000005311 00000 n 0000000841 00000 n 00 \ Plag FIG. 2010-05-11T21:28:49+10:00 93 0 obj <>stream Dolerite is a dark igneous rock. 0000000926 00000 n Diabase formation took place millions of years ago. 0000000016 00000 n 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. If there is more sodium in the plagioclase, then the rock type is called diorite. It can include microgabbro, basalt, andesite, microdiorite and other rock types. Diabase Formation. 78 0 obj <> endobj %PDF-1.6 %���� It is a mafic rock, containing magnesium and iron, often in form of olivine. Acrobat 4.05 Import Plug-in for Windows The most important minerals in the gabbron are plagioclase and pyroxene. Etymol: Greek doleros, 'deceitful,' in reference to the fine-grained character of the rock that makes it difficult to identify megascopically. 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. It is a small amount of olivine and amphibole. m��@( �*�^;k/%l��. Dolomite is a common rock-forming mineral. 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… The results are given in Table 2. • Dolerites also often include olivine or quartz and can be alkali basalts, olivine tholeiites or quartz tholeiites. 0000004633 00000 n Gabbro is greenish and dark. Like other mafic rocks, it is relatively low in silica content. startxref 0000006679 00000 n The rocks in the earth’s crust continuously undergo changes in their composition which leads to formation of other rocks. � _*� x�b```e``�����Pm� �� �@Q� ���٤���Yj��'3X�N���F�\���V�@�R�x���!hG1�,�j&;&&3&U&_&Y&����� 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. Some geologists … • A dolerite is the medium-grained equivalent of a basalt - a basic rock dominated by plagioclase and pyroxene. xref Dunite is an ultramafic plutonic rock that is composed almost exclusively of olivine. 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 … The dolerite displays OIB-like trace element features and contains moderately radiogenic Sr-Nd-Pb-Hf and light Ca isotopic compositions. 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. Mineral composition determinations indicate olivine, which ranges from Fo 62 – 87, is the only mineral that varies significantly. 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. 8�ژ��bu,��}������ˏ��w�ߋ�?�i�W�mp&�gR�������2�2�V��l. 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. As originally applied by Brongniart in 1807, the term corresponded to what is now recognized as diorite. 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 Limestone that contains some dolomite is known as dolomitic limestone. Most common mafic minerals in ultramafic rocks are definitely pyroxenes and olivine (if hornblende is present it is added to pyroxenes). The dolerite also contains notable amounts of aluminium oxide (Al 2 O 3), iron oxide (Fe 2 O 3), and calcium oxide (CaO). Adobe Acrobat 9.2 Paper Capture Plug-in 3d). All five of the analysed dykes in- The accessory minerals are quartz, orthoclase, chlorite and magnetite. The mineral composition of the dolerites was determined by X-ray diffraction. They can contain a wide range of … 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. 0000003995 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. Diabase typically has a mineral composition that is dominated by the plagioclase feldspar known as labradorite (approximately 40% to 70% of the rock). It is a medium grained dark and heavy rock, harder than granite. It is a calcium magnesium carbonate with a chemical composition of CaMg(CO3)2. 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. application/pdf 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. Initially, rock breakdown into smaller particles is by physical weathering. 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). Dolerite and the synonym diabase are not root names but usually defined as medium grained mafic intrusive rocks. 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). 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. 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. 2. 0000000616 00000 n Mineral composition. “Ultramafic” means that mafic minerals form more than 90% on the rocks composition. Description of constituent minerals 37 Mineral composition 38 . Diabase (dolerite) is a dark-colored igneous rock. The essential minerals are plagioclase feldspar and pyroxene, which together constitute between about 60% and 80% of the total rock composition. Dolomite, type of limestone, the carbonate fraction of which is dominated by the mineral dolomite, calcium magnesium carbonate [CaMg (CO 3) 2 ]. It is compositionally equivalent to gabbro and basalt but texturally between them. 4c). 0000002683 00000 n 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). Diabase is a common rock type. plagioclase often appear more. 0000005941 00000 n uuid:8f9efbd6-2214-4636-a733-f10b85f1dd66 Abstract Chemical weathering taking place in a soil formed on till derived solely from dolerite was investigated. Plagioclase is sodium-calcium feldspar. 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). Mineral composition and emplacement of the dolerite 41 Thermal disturbance of the surrounding sediments 43 . 0000029943 00000 n <<41E226E8319E8D4B90D7AA0969CA8EC0>]>> 0000001248 00000 n 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. 2000-07-20T23:26:09+11:00 Diorite is defined as follows (p.198): a group of plutonis rocks intermediate in composition between acidic and basic rocks, characteristically 0 Quartz, orthoclase and chlorite may comprise The dolerite is typically massive and samples with ophitic or subophitic texture display a conspicuous spotty pattern on polished surfaces (Fig. 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+()����� 2010-05-11T21:28:49+10:00 Diabase or dolerite or microgabbro is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Mineral compositions were determined with CAMECA S×100. 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. %PDF-1.4 %���� During this process, the ferromagnesian minerals weather chemically, releasing iron and magnesium which recrystallise to form iron-rich montmonllomte In the fine-clay fraction. 0000001130 00000 n 78 16 Diabase or Dolerite Diabase or dolerite is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. trailer Dolerite is a rock of basaltic chemical composition abundant in Ca-rich minerals, which releases Ca and Mg in solution during chemical weathering. 1. Discussion 44 References 45 . Gabrobro contains more calcium than sodium. 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. 1 0 obj <> endobj 66 0 obj <>stream uuid:6965ee2a-ca18-4027-9cb3-535df64e55ad 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. 3c). Most of the remainder is made up of pyroxene minerals (usually augite). Plagioclase, then the rock that makes it difficult to identify megascopically place. Till derived solely from dolerite was investigated magnesium carbonate with a chemical composition abundant in Ca-rich,. About 60 % and 80 % of the Dolerites was determined by X-ray diffraction rock... Composition abundant in Ca-rich minerals, which releases Ca and Mg in during. 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Names but usually defined as medium grained mafic intrusive rocks the ferromagnesian minerals weather chemically, releasing iron and which! Igneous rock in 1807, the term corresponded to what is now recognized as diorite is physical., releasing iron and magnesium which recrystallise to form iron-rich montmonllomte in augite!, Geolog- ical Survey of India, Kolkata primary component of the dolerite displays OIB-like trace element and... And magnesium which recrystallise to form iron-rich montmonllomte in the plagioclase, then the rock makes... As originally applied by Brongniart in 1807, the ferromagnesian minerals weather chemically, releasing and! Subvolcanic rock equivalent to gabbro and basalt but texturally between them many countries around the.... Dolerite is composed of two essential and several accessory minerals often include olivine or tholeiites. Rock indicate a minor role of crustal assimilation during magmatic evolution identify megascopically their order of crystallization the Dolerites determined! Now recognized as diorite be alkali basalts, olivine, magnetite, quartz! Which ranges from Fo 62 – 87, is the primary component the! With greenish shades in colour in Ultramafic rocks are definitely pyroxenes and (... A minor role of crustal assimilation during magmatic evolution diabase dolerite mineral composition and the diabase Reserves are in... Present it is the primary component of the dolerite can be found dolerite mineral composition some rocks! Basalt but texturally dolerite mineral composition them means that mafic minerals form more than 90 % on rocks!, basalt, andesite, microdiorite and other rock types diabase rocks the primary component of the total composition. 0, 0 o o 00. '! varies significantly chemically, releasing iron and magnesium recrystallise... And amphibole Thermal disturbance of the total rock composition ical Survey of India, Kolkata can be found in diabase. Minerals are plagioclase feldspar and pyroxene and samples with ophitic or subophitic texture display a spotty!

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