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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
- IIT JAM
- Geology (GG)
Question below
2 Answer(s)
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Rahul kumar
Diagramatic representation of the rock.
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Rahul kumar Best Answer
Ans: Lherzolite; In the given rock the modal composition of mafic minerals (Olivine+opx+cpx) is 97%, which is greater than 90% that's why we will use IUGS classification of ultramafic rocks. Normalising tha modal composition of Olivine, Opx and Cpx to 100% will give, Olivine= (63/97) × 100 = 65%, Opx= (16/97) × 100= 16.5%, Cpx= (18/97) × 100= 18.5%. This modal composition will lie somewhere in Lherzolite field as shown in the rock. So the rock name is Lherzolite. NOTE: The sum of given modal composition in question is greater than 100%, which is not possible so the composition of others must be less than 10% i.e., modal composition of others= 100 - (Olivine+Opx+Cpx)= 100- (63+16+18) = 3%
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Sajan sarthak
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Lherzolite see the attached figure and develop the imagination
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i know the answer lherzolite how it will be also i knew sir.but i wanted a perfect answer to clear my doubts.
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perfect answer means olivine is greater than 40 percentage so it can be hazburgite ,lehrzolite,or wehrlite but again opx an cpx are almost same like greater than 10 percentage so the field it will fall in lehrzolite .
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Rahul kumar
As I have stated in answer, the modal composition of all minerals (olivine+Opx+Cpx+Others) is greater than 100%, which is wrong because modal composition can't be greater than 100%. If you will consider the modal composition of Olivine, Opx and Cpx as 63, 16 and 18% respectively then the modal percentage of other minerals must be 100-(Olivine+Opx+Cpx) = 100-97= 3%.