This set of Engineering Geology Multiple Choice Questions & Answers (MCQs) focuses on “Formation and Descriptive Study of Minerals – 01”.
1. Which mineral group is abundantly found in the earth’s crust?
a) Mica group
b) Felspar group
c) Oxide group
d) Silicate group
View Answer
Explanation: The felspars (The feldspars in American technology) are the most prominent group of minerals making more than fifty percent, by weight, crust of the Earth up to a depth of 30 km.
2. Felspar is found abundantly or in majority in which kind of rock?
a) Igneous rocks
b) Sedimentary rocks
c) Metamorphic rocks
d) Fossil rocks
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Explanation: Felspars occur chiefly, in the igneous rocks (more than 60 percent) but also occur in good proportion in the metamorphic rocks. Felspars are also found in some sedimentary rocks like arkose and greywacks.
3. The chemical composition of the feldspar group is __________
a) Oxide
b) Aluminates
c) Silicates
d) Aluminosilicates
View Answer
Explanation: In chemical composition, felspars are chiefly aluminosilicates (also referred as alumosilicates) of Na, K and Ca with the following general formula, WZ4O8, in which W=Na, K, Ca and Ba and Z= Si and Al.
4. In the atomic structure, each oxygen atom is shared by how many tetrahedra?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: At atomic level, the felspars show a continuous three-dimensional network type of structure in which the SiO4 tetrahedra are linked at all the corners, each oxygen ion begin shared by two adjacent tetrahedral.
5. The crystallographic system shown by felspar group is __________
a) Monoclinic
b) Triclinic
c) Rhomboclinic
d) Monoclinic and triclinic
View Answer
Explanation: The felspar group of minerals crystallise only in two crystallographic systems: Monoclinic and triclinic. Infact, the plagioclase division of felspars crystallizes only in triclinic system.
6. How many groups are the felspar minerals classified into, on the basis of chemical composition?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: Felspars are classified both on the basis of their chemical composition and also on their mode of crystallization, Chemically, felspars fall into two main groups: the potash felspars and the soda lime felspars.
7. The felspar minerals are free from __________
a) Iron
b) Iron and manganese
c) Magnesium
d) Iron and magnesium
View Answer
Explanation: The felspar group minerals are generally light in colour, because of the absence of Fe and Mg. The minerals have lower specific gravity (generally around 2.6), have doubly cleavage and a hardness varying between 6-6.5.
8. What is the chemical composition of Orthoclase?
a) K Al O8
b) Ca Al Si3O8
c) K Al Si3 O8
d) Ca Al O8
View Answer
Explanation: Orthoclase mineral has the specific gravity around 2.56 to 2.58. Its chemical composition is K Al Si3O8. It is the most common and essential constituent of many igneous rocks, especially granite.
9. What is the distinguishing characteristic of microcline and orthoclase?
a) Colour
b) Streak
c) Chemical composition
d) Hardness
View Answer
Explanation: Both orthoclase and microcline have same colour but microcline gives white streak whereas, orthoclase does not give any streak. Chemical composition and hardness are almost same for both the minerals.
10. Which of the following is not true about plagioclase?
a) It is composed of K mainly
b) It is composed of either Na, Ca, or Al
c) It is of massive or crystalline structure
d) It gives 2 sets of cleavages
View Answer
Explanation: Plagioclase is usually composed of either Na or Ca or Al or combination of them. K is present in orthoclase and not in plagioclase.
11. Microcline can be easily distinguished from orthoclase.
a) True
b) False
View Answer
Explanation: The microcline mineral is not easily distinguished in hand specimens from orthoclase except when perfectly crystallized.
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