UPSC Previous Year Question Paper 2026-Combined Geo-Scientist (Main) Examination,-GEOLOGY II - With Free PDF download Link

1. Answer the following questions in brief : 5×10=50

(a) State the symmetry elements of the crystal class 4/m2/m2/m4/m2/m2/m and plot the crystal face (110) on its stereogram.

(b) State the condition in which a biotite grain appears non-pleochroic under microscope.

(c) How are the elements belonging to different categories of Goldschmidt's classification broadly distributed in the periodic table?

(d) Calculate the ratio of the number of atoms of daughter isotope to the number of atoms of parent isotope after the elapse of 3 half-lives.

(e) Discuss the source rocks of A-type and M-type granite.

(f) What is the mineralogical composition of picritic basalt?

(g) Define entropy (s) and state how it is calculated.

(h) What is devolatization reaction in metamorphism? Write with suitable examples.

(i) Give the most ongoing striking changes in the Earth's magnetic field since the last few thousand years.

(j) What causes drop in S-wave velocity and increase in attenuation of seismic energy at low-velocity zone?

UPSC Previous year question paper Geo scientist exam

SECTION-B

Attempt any one question.

1. (a) Describe the process of calculation of Miller indices of a crystal face. Determine the Miller indices of the following crystal faces :

(i) A crystal face which intersects aa , bb , cc axes at 2, 3, 4 unit distances (ii) A crystal face which intersects aa and bb axes at 1 and 5 unit distances and is parallel to cc -axis (iii) A crystal face which intersects bb -axis at 2 unit distance and is parallel to aa and cc axes

Are these three crystal faces tautozonal? 6+9=15

(b) Why are some minerals optically isotropic and others anisotropic? Name seven crystal systems. Which minerals of these seven crystal systems are isotropic, anisotropic uniaxial and anisotropic biaxial? Write with reason and suitable examples. 4+2+9=15

1. (a) Give ternary diagram for feldspar classification and explain cationic substitution in plagioclase. 5+5=10

(b) How do structure and composition of kaolinite and smectite groups differ from each other? 5+5=10

(c) Give distinguishing physical properties of the following mineral groups : 5+5=10

(i) Pyroxene and Amphibole (ii) Quartz and Feldspar

UPSC Previous year question paper Geo scientist exam

1. (a) Under what conditions can the variation of partial pressure (Pi)(Pi​) of a component ii with its mole fraction (Xi)(Xi​) in a mixture be explained by (i) the Raoult's law and (ii) the Henry's law? 8+7=15

(b) If a mafic crust containing 10μg/g10μg/g of element Li undergoes 10%10% equilibrium partial melting (batch melting), then what will be the concentration of Li in the resulting melt? Assume that the bulk distribution coefficient of Li for mafic composition is 0.250.25 (D=0.25)(D=0.25) . 15

1. (a) How are the concentrations of rare earth elements (REEs) in a natural sample generally plotted? Why are these concentrations normalized to a reference material? 5+5=10

(b) Define ϵNDϵND​ (epsilon-ND). How do ϵNDϵND​ and Sr isotopic ratio (87Sr86Sr)(86Sr87Sr​) taken together help to understand the origin of an igneous rock? 10

(c) Results of stable isotope measurements in a natural sample are generally presented in δδ (delta) notation. How is δδ defined? Derive a relationship between the fractionation factor (α)(α) and δδ . 10

UPSC Previous year question paper Geo scientist exam

SECTION-D

Attempt any one question.

1. (a) How is viscosity of a silicate magma related to its temperature (T)(T) , silica (SiO2)(SiO2​) content and H2OH2​O content? Write with reason and suitable examples. 15

(b) Discuss the magmatic differentiation due to sequential fractionation of minerals from a basaltic magma. Define co-magmatic suite of rocks with suitable examples. 12+3=15

1. (a) Define alkaline rocks. Discuss the various causes of alkali enrichment in these rocks. How does one explain the origin of alkaline rocks in continental rift zone? 2+8+5=15

(b) What are the differences of layered and massive anorthosite? Discuss the different ideas put forward to account for the origin of massive anorthosite. 7+8=15

UPSC Previous year question paper Geo scientist exam

SECTION-E

Attempt any one question.

1. (a) State the different factors of metamorphism and briefly discuss the types of metamorphism caused by these factors. 3+12=15

(b) Define Gibbs free energy (G)(G) and state how it is related to chemical potential (μ)(μ) . Deduce the relationship of GG with temperature (T)(T) and pressure (P)(P) . 5+10=15

1. (a) What are the components used in AFM projection of metamorphic rocks? How does one calculate 'A', 'F', 'M' values? Discuss the procedure of plotting mineral assemblages of metapelitic rocks on AFM diagram with reason. 15

UPSC Previous year question paper Geo scientist exam

6+1+8=15

[Figure: Pressure-Temperature diagrams (i)-(iv)]

SECTION-F

Attempt any one question.

1. (a) Explain and illustrate with figures the physiographic features and fault styles that occur along multiple segments of continental transform. 15

(b) Explain the flow mechanism in ductile rocks. 15

1. (a) Explain the nature of deformation along the regions A,B,CA,B,C and DD in the figure of Benioff zone : 10

[Figure: Benioff zone diagram with regions a, b, c, d]

(b) Give reasons and illustrate with figures for heterogeneity in heat flow along the mid-oceanic ridges. 10

(c) Explain and illustrate with figures the motion of particles within a material on the passage of body and surface waves. 10

UPSC Previous year question paper Geo scientist exam

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