Granite

Granite

1. GRANITE

2. contents Introduction Mineralogy Textures Mode of occurrences Types Occurrences Reference conclusion

3. The word "granite" comes from the  Latin   granum , Granite   is a common type of plutonic   intrusive ,  felsic ,  igneous   rock  which is granular and  phaneritic  in texture. This rock consists mainly of  quartz ,  mica , and  feldspar . By  definition , granite is an igneous rock with at least 20% quartz by volume.   Outcrops  of granite tend to form rounded  massifs . Granites sometimes occur in circular  depressions  surrounded by a range of hills. Granite is nearly always massive ,hard and tough, and therefore it has gained widespread use as a construction stone. The average  density  of granite is between 2.65 and 2.75 g/cm 3 ,Melting temperature is 1215 - 1260 °C. Introduction

4. Essential minerals Feldspar and quartz are the most important mierals Quartz makes up about 10-30% it is anhedral and occur as phenocryst Feldspar -alkali feldspar,orthoclase,microcline MINERALOGY Quartz Orthoclase Feldspar

5. Accessory minerals Biotite –common mafic mineral in granites.colour varies with fe content. Hornblende-green hornblende seen in calcalkali granites amphibole Pyroxene Hedenbergite Minor accessories Tourmaline,( schorl rock) topaz,epidote,garnet ( almandine,spessartine ), apatite,epidote

6. QAPF Diagram

7. Granite is classified according to the  QAPF diagram  for coarse grained  plutonic rocks  and is named according to the percentage of quartz , alkali  feldspar  ( orthoclase ,  sanidine , or  microcline ) and  plagioclase  feldspar. Granite differs from  granodiorite  in that at least 35% of the  feldspar  in granite is  alkali feldspar  as opposed to  plagioclase ; it is the alkali feldspar that gives many granites a distinctive pink color. When a granitoid contains less than 10% orthoclase, it is called  tonalite ;  pyroxene and   amphibole  are common in tonalite . A granite containing both muscovite and biotite   micas  is called a binary or  two-mica  granite . Two-mica granites are typically high in  potassium  and low in plagioclase , and are usually S-type granites or A-type granites. The volcanic  equivalent of granite is  rhyolite and hypabyssal is granophyre (Tyrrell’s classification)

8. Granite is a phanerocrystalline rock which is medium to coarse grained. They also in holocrystaline , hypidiomorphic , granular rocks Some granites exhibit porphyritic texture( phenocryst -feldspar), orbicular texture, graphic( qtz & fldspr ), granophyric texture Occasionally some individual crystals ( phenocrysts ) are larger than the groundmass , in which case the texture is known as  porphyritic . A granitic rock with a  porphyritic texture  is sometimes known as a  porphyry . Granites can be pink to gray in color, depending on their chemistry and mineralogy. TEXTURE

9. Granites occur as huge batholiths of great dimensions usually occuring in the cores of mountain ranges( stocks,bosses,laccoliths ) The huge bodies does not show any peculiar structure Moral jointing is common and rift and grain is also present in most varieties. The basic minerals like biotite,amphibole occur as seggregations and patches in the granite body.sometimes parallel arrangement of minerals(foliation) may be seen Mode of occurrence

10. Mica granite – the micas,muscovite and biotite together make up 10% of the rock. other accessory minerals are allanite, sphene, apatite, magnetite and guorite. It is the most abundant type of granite. Biotite hornblende granite – these are next in abundance. These rocks are somewhat more basic. A few of them carry pyroxenes . Pyroxene granite- this type is rare. Biotite and hornblende are entirely absent here or make up only vary small amount.clinopyroxene is the chief mafic minerals. Orbicular granite – it exhibits orbicular structure. The orbicules are made up of layers of biotite and quartz. Granite, pegmatites and aplites – these are very common in and around a granitic body. The pegmatites have the intergrowth texture and are very coarse grained. They are store house of a number of valuable minerals. The aplites are finegrained , equigranular , allotriomorphic rocks. They occur as contact facies in a granitic body. Types

11. Alkali granite – this is a granite marked by the occurrence of amphibole and puroxene rich in Na and Fe. The rock is usuallymade up of sodic and potassic feldspars(75%). perthite is common. Aegerine and riebeckite are the common mafics . Accessories are apatite,sphene,zircon,iron ore etc. Porphyritic granite – exhibits the porphyritic texture. Phenocrysts are orthoclase, microcline, perthite .

12. Granite and granite gneiss are too common in peninsular India and cover vast areas in Indian geology. Typical granite occurrences are Singhbhum granite(Bihar), Bundelkhand granite(Rajasthan), Erinpura granite, Idar granite, Closepet granite, Chamundi granite(Karnataka). Granites of North arcot and Sankaridrug in Tamilnadu and granites of Himalayas.alkali granite are seen in Siwana and Tatanagar . Indian occurrences

13. It is a coarse-grained structure of such a  crystalline  rock. Granite is usually found in the  continental plates  of the Earth's crust(magma). This rock consists mainly of  quartz ,  feldspar , mica etc   (Curling) another name for a granite stone. A common, coarse-grained, light-colored, hard igneous rock consisting chiefly of quartz, orthoclase or microcline, and mica, used in monuments and for building. conclusion

14. Igneous and metamorphic petrology(1962), Francis J.Turner,McGraw-Hill book company. http://en.wikipedia.org/wiki/Granite http://www.thefreedictionary.com/granite Reference