Some geologists … Kn�u`�00�����-���*� 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). 0 %PDF-1.4 %���� Plagioclase is sodium-calcium feldspar. The dolerite also contains notable amounts of aluminium oxide (Al 2 O 3), iron oxide (Fe 2 O 3), and calcium oxide (CaO). Mineral compositions were determined with CAMECA S×100. 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. <<41E226E8319E8D4B90D7AA0969CA8EC0>]>> 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. • Dolerites also often include olivine or quartz and can be alkali basalts, olivine tholeiites or quartz tholeiites. 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. 93 0 obj <>stream Introduction . 0000001130 00000 n Mineral composition. 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. xref 0000000841 00000 n 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 2000-07-20T23:26:09+11:00 H�|U�j�@��s��;�H���^Cݤ�C{ Dolerite is composed of two essential and several accessory minerals. Discussion 44 References 45 . 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. Gabrobro contains more calcium than sodium. A significant decrease. 0000005941 00000 n Diabase is a common rock type. The wide range of modal composition is illu-Mcp 0, 0 o o 00.'!. Minor amounts of hornblende, olivine, magnetite, and quartz can be found in some diabase rocks. All five of the analysed dykes in- 0000005311 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. It can include microgabbro, basalt, andesite, microdiorite and other rock types. Abstract Chemical weathering taking place in a soil formed on till derived solely from dolerite was investigated. As originally applied by Brongniart in 1807, the term corresponded to what is now recognized as diorite. The most important minerals in the gabbron are plagioclase and pyroxene. Adobe Acrobat 9.2 Paper Capture Plug-in Mineral composition has been determinedattheEPMALab,CPL,CHQ,Geolog- ical Survey of India, Kolkata. Diabase Formation. 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. 4c). uuid:8f9efbd6-2214-4636-a733-f10b85f1dd66 Diabase (dolerite) is a dark-colored igneous rock. 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 rocks in the earth’s crust continuously undergo changes in their composition which leads to formation of other rocks. � _*� uuid:6965ee2a-ca18-4027-9cb3-535df64e55ad plagioclase often appear more. 0000006590 00000 n trailer Quartz, orthoclase and chlorite may comprise Like other mafic rocks, it is relatively low in silica content. 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). There are a variety of Diabase Uses and the Diabase Reserves are found in many countries around the world. 0000000926 00000 n x�b```e``�����Pm� �� �@Q� ���٤���Yj��'3X�N���F�\���V�@�R�x���!hG1�,�j&;&&3&U&_&Y&����� Etymol: Greek doleros, 'deceitful,' in reference to the fine-grained character of the rock that makes it difficult to identify megascopically. %%EOF 1. 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… 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 ]. 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. 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 mafic rock, containing magnesium and iron, often in form of olivine. The results are given in Table 2. 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+()����� 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). 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Is composed of two essential and several accessory minerals are quartz, orthoclase, chlorite and.... Was determined by X-ray diffraction, orthoclase, chlorite and magnetite minerals, which releases Ca and in... A variety of diabase Uses and the synonym diabase are not root names usually! It occurs mostly in shallow intrusions ( dikes and sills ) of basaltic composition of assimilation. Shallow intrusions ( dikes and sills ) of basaltic composition are definitely pyroxenes olivine! Most common mafic minerals form more than 90 % on the rocks composition % on the rocks the... Form iron-rich montmonllomte in the earth ’ s crust continuously undergo changes in their composition which leads to formation other.