Question
Match the alkaline rocks listed in Group I with their characteristics listed in Group II Group I Group II (P) Basanite (1) Volcanic rock lacking feldspar (Q) Nephelinite (2) Ultrapotasic volcanic rock (R) Shonshonite (3) Feldspathoid-bearing basalt (S) Lamproite (4) K-rich basalt
The correct answer is
P-3; Q-1; R-4; S-2
This question requires matching specific alkaline rocks from Group I with their defining characteristics from Group II.
Matching Alkaline Rocks and Characteristics
We need to match the rocks in Group I (Basanite, Nephelinite, Shonshonite, Lamproite) with their corresponding descriptions in Group II.
Group I: Alkaline Rocks
- (P) Basanite
- (Q) Nephelinite
- (R) Shonshonite
- (S) Lamproite
Group II: Characteristics
- (1) Volcanic rock lacking feldspar
- (2) Ultrapotassic volcanic rock
- (3) Feldspathoid-bearing basalt
- (4) K-rich basalt
Step-by-Step Matching
- Basanite (P): Basanite is a volcanic rock chemically equivalent to alkali basalt or basalt but is richer in feldspathoids (like nepheline or leucite) and poorer in plagioclase. This fits characteristic (3) Feldspathoid-bearing basalt. So, P-3.
- Nephelinite (Q): Nephelinite is an ultramafic volcanic rock composed primarily of nepheline and clinopyroxene. It specifically lacks feldspar, making characteristic (1) Volcanic rock lacking feldspar the correct match. So, Q-1.
- Shonshonite (R): Shonshonite is a variety of syenite or trachyte, known for being rich in potassium (K-rich). It can be considered a type of K-rich basalt in broader classifications. Therefore, characteristic (4) K-rich basalt is the best fit. So, R-4.
- Lamproite (S): Lamproites are a group of ultrapotassic volcanic rocks. They are characterized by high potassium oxide and magnesium content, and typically contain specific minerals like olivine, phlogopite, and certain pyroxenes. Characteristic (2) Ultrapotassic volcanic rock accurately describes lamproite. So, S-2.
Final Matching
Based on the step-by-step analysis:
- Basanite (P) matches Feldspathoid-bearing basalt (3).
- Nephelinite (Q) matches Volcanic rock lacking feldspar (1).
- Shonshonite (R) matches K-rich basalt (4).
- Lamproite (S) matches Ultrapotassic volcanic rock (2).
The correct matching is P-3; Q-1; R-4; S-2.
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Important Questions from Igneous Petrology (Classification, Forms, Textures, Genesis)
- Match the rock types in Group-I with their most likely corresponding lithospheric / tectonic settings of formation in Group-II
Group-I Group-II P. Boninite 1. Continental anorogenic Q. Lamproite 2. Island-arc R. Phonolite 3. Continental collision S. Leucogranite 4. Intraplate oceanic - The mole percentages of SiO$_2$, Al$_2$O$_3$ and K$_2$O in a granitic rock are 84.21, 7.89 and 7.89, respectively. The molar proportion (in %) of K-feldspar in the rock is ________ [ round off to one decimal place]
- Which one of the following is a mafic volcanic rock?
Match the following igneous textures in Group-I with their definitions in Group-II.
Group-I
Group-II
P Vitrophyre 1 Alkali feldspar rimmed by plagioclase Q Rapakivi 2 Aggregate of radially arrayed, needle-like crystals of plagioclase with or without clinopyroxene R Ocelli 3 Sub-parallel skeletal, platy olivine and/or pyroxene S Spinifex 4 Large phenocrysts within a glassy matrix - Which one of the following statements about igneous rocks is CORRECT?
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