This set of Engineering Geology Multiple Choice Questions & Answers (MCQs) focuses on “Composition and Texture of Igneous Rocks – 01”.
1. Pick the option which does not determine the texture of igneous rocks.
d) Arrangement of the constituents within the body of the rock
Explanation: The term texture is defined as the mutual relationship of different mineralogical constituents in a rock. It is determined by the size, shape and arrangement of these constituents within the body of the rock.
2. Which of the following is not a factor explaining texture?
a) Wind conditions
b) Degree of crystallization
Explanation: The following three factors will primarily define the type of texture in a given igneous rock: Degree of crystallization, Granularity and Fabric.
3. The degree of crystallization where the constituents are very fine or glassy are
Explanation: Holohyaline is the term used, when, all the constituents are very fine in size and glassy or non-crystalline in nature.
4. What is the term used when constituents are crystallized completely?
Explanation: Holocrystalline is the term used when all the constituent minerals are distinctly crystallized.
5. What is the range of grain size for coarse grained igneous rock?
a) Above 2 mm
b) Below 2 mm
c) Above 5 mm
d) Below 5 mm
Explanation: When the average grain size is above 5 mm; the constituent minerals are then easily identified with naked eye. These rocks are termed as coarse-grained rock.
6. Grain size 5mm to 1mm is termed as
a) Coarse grained
b) Intermediate grained
c) Fine grained
d) Medium grained
Explanation: When the average grain size lies between 5 mm to 1 mm it is termed as medium grained. Use of magnifying lens often becomes necessary for identifying all the constituent mineral components.
7. The grain size involving use of microscope is
a) Coarse grain
b) Medium grain
c) Fine grain
d) Very coarse grain
Explanation: When the average grain size is less than 1 mm it is termed as fine grain. In such rocks, identification of the constituent mineral grains is possible only with the help of microscope for which very thin rock sections have to be prepared.
8. What is the term given when some granules are exceptionally large and few are small?
a) Mixed granular
Explanation: The texture is termed as equigranular when all the component minerals are of approximately equal dimensions and as inequigranular when some minerals in the rock are exceptionally larger or smaller than the other.
9. Pick the wrong statement about granitic texture.
a) The constituents are coarse grained
b) The constituents are medium grained
c) The crystals show euhedral to subhedral outlines
d) The rock is microgranular
Explanation: In the granitic texture, the constituents are either all coarse grained or all medium grained and the crystals show euhedral to subhedral outlines.
10. The number of equigranular textures are
Explanation: All those textures in which majority of constituent crystals of a rock are broadly equal in size are described as equigranular textures. There are 3 types- Granitic, Felsitic and Orthophyric.
Sanfoundry Global Education & Learning Series – Engineering Geology.
To practice all areas of Engineering Geology, here is complete set of 1000+ Multiple Choice Questions and Answers.