The question describes a specific type of igneous rock characterized by its composition and mineralogy.
Identifying Kimberlite Rock
The key identifiers provided are:
- Composition: Potassic, ultrabasic, hybrid igneous rock.
- Macrocrysts: Olivine, Cr-rich diopside (a pyroxene), phlogopite (a mica), and pyrope (a garnet).
- Groundmass: Serpentine, carbonate, and perovskite.
Mineralogical Comparison
This specific combination of minerals is characteristic of kimberlite. Kimberlites are known for being ultrabasic and often potassic, containing mantle-derived xenocrysts and xenoliths. The listed minerals, including olivine, Cr-diopside, phlogopite, pyrope, and perovskite, are commonly found in kimberlites. The groundmass often consists of serpentine and carbonate minerals due to secondary alteration processes.
Evaluating Other Options
- Ijolite: Typically composed of melilite and nepheline; does not match the described mineralogy.
- Melilitolite: Primarily composed of melilite; differs significantly from the description.
- Harzburgite: An ultrabasic rock composed mainly of olivine and orthopyroxene; lacks the characteristic potassic minerals (phlogopite, perovskite) and specific pyroxene/garnet types mentioned.
Therefore, based on the unique mineral assemblage, the rock described is kimberlite.
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?
