Engineering Geology Questions and Answers – Forms of Igneous Rocks – 01

This set of Engineering Geology Multiple Choice Questions & Answers (MCQs) focuses on “Forms of Igneous Rocks – 01”.

1. Form of igneous rock where magma is injected and cooled along planes of host rocks is ______________
a) Discordant bodies
b) Concordant bodies
c) Parallel bodies
d) Synchronous bodies
View Answer

Answer: b
Explanation: All those intrusions in which the magma has been injected and cooled along or parallel to the structural planes of the host rocks are called concordant bodies.

2. Pick the type of concordant body among the following.
a) Batholith
b) Extrusion
c) Dykes
d) Phacolith
View Answer

Answer: d
Explanation: The various types of concordant bodies are sills, phacoliths, laccoliths and lopoliths.

3. The type of concordant body whose thickness is much smaller than its length and width is ______________
a) Sill
b) Phacolith
c) Dyke
d) Laccolith
View Answer

Answer: a
Explanation: It is typical of sills that their thickness is much small than their width and length. Moreover, this body commonly thins out or tapers along its outer margins.
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4. The upper and lower margins of sills are relatively ______________
a) Coarser grain size
b) Medium grain size
c) Finer grain size
d) Can be of any size
View Answer

Answer: c
Explanation: The upper and lower margins of sills commonly show a comparatively finer grain size than their interior portions.

5. Sills in length are restricted to hundreds of metres.
a) True
b) False
View Answer

Answer: b
Explanation: In length, sills may vary from a few centimeters to hundreds of meters. Minor and local projections from big sills may rise above into the overlying strata.

6. Most common rocks composing the sills are ______________
a) Marbles
b) Shales
c) Gabbros
d) Granites
View Answer

Answer: c
Explanation: The most common rocks composing the sills are intermediate and basic igneous rocks like syenites and gabbros. They may show aphinitic and porphyritic textures.

7. The small sized intrusives that occupy bends in the folds are called ______________
a) Sills
b) Lopolith
c) Laccolith
d) Phacolith
View Answer

Answer: d
Explanation: Phacoliths are concordant, small sized intrusions that occupy positions in the troughs and crests of bends called folds.
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8. The concordant bodies associated with structural basins are ______________
a) Sills
b) Lopolith
c) Laccolith
d) Phacolith
View Answer

Answer: b
Explanation: Those igneous intrusions, which are associated with structural basins, that are sedimentary beds inclined towards a common centre, are termed as lopoliths. They may form huge bodies of consolidated magma.

9. The shape arch or dome is shown by which type of concordant body?
a) Sills
b) Lopolith
c) Laccolith
d) Phacolith
View Answer

Answer: c
Explanation: Laccoliths are concordant intrusions due to which the invaded strata have been arched up or deformed into a dome. The igneous mass itself has a flat or concave base and a dome-shaped top.
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10. What is the type of lava which leads to the formation of laccolith?
a) Viscous
b) Non-viscous
c) Partially crystallized
d) Gaseous lava
View Answer

Answer: a
Explanation: Laccoliths are formed when the magma being injected is considerably viscous so that it is unable to flow and spread for greater distances. Instead, it gets collected in the form of a heap about the orifice of an eruption.

11. What is the type of laccolith in which fracture is formed?
a) Dyke
b) Batholith
c) Bysmalith
d) Volcanic neck
View Answer

Answer: c
Explanation: Extreme types of laccoliths are called bysmaliths and in these the overlying strata get ultimately fractured at the top of the dome because of continuous injections from below.

12. A sill is not considered to be a sill when two or more injections of different types of magma are involved.
a) True
b) False
View Answer

Answer: b
Explanation: Composite sills are the sills which result from two or more injections of different types of magma. Hence it cannot be told that it is not a sill, instead, it is a type of sill.

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.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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