STUDY OF IMPORTANT METAMORPHIC ROCKS.pdf

Submitted By - Ritisha Singh
Department of Geology
M.Sc 2nd
Sem

C O N T E N T S
1) Granulite
2) Khondalite
3) Eclogite
4) Migmatite
5) Gondite
6) Charnockite

G R A N U L I T E
Petrological Characteristics
1. Fine to medium grained metamorphic rock.
2. Derived from plutonic metamorphism.
3. Typically light coloured rocks
4. Consists of feldspar and quartz grains, frequently with
abundant pyroxene and garnet, and occasionally sillimanite,
kyanite, green spinel, etc., in small quantity.
5. Granoblastic texture with granulose to sometimes gneissose
structure (Granulite facies).

Indian Stratigraphic Position
Archean basements of Peninsular India, eg. Sausar Group’s Tirodi
Biotite Gneiss and Eastern Ghats Belt.
Locality
Nilgiri hills, Eastern ghats, etc.
Economic Importance
In construction of roads, bridges and buildings, etc.
Image Source :
https://www.alexstrekeisen.it/english/meta/maficgranu
lite.php

Facts/ Other Importance
The type location for granulite is the Granulitgebirge in Saxony,
eastern Germany.
It was here that the term "granulite" first appears in the literature
(Weiss, 1803). But the word "granulite" is older, it was invented by the
German writer Johann Wolfgang von Goethe (1785)
Considered to be good analogues of middle to lower Crustal rocks.
Their study is hence important in understanding deep crustal and
crust-mantle interaction processes.

Image Source :
https://www.alexstrekeisen.it/english/meta/
maficgranulite.php
Charnockite patches in granulite gneiss.
Image Source : https://www.alexstrekeisen.it/english/meta/maficgranulite.php

K H O N D A L I T E
1. A garnet-sillimanite-quartz-K feldspar gneiss with or without
graphite. Biotite or rutile is noticed occasionally. Plagioclase is also
minor but important constituent in some varieties. Also contains
manganese in some varieties like rhodonite.
2. Presence of quartzite bands within khondalite and variation of mineral
proportions in khondalite strongly indicate the sedimentary nature of
the precursor.
3. Biotite bearing assemblage is a product of chemical variation in the
protolith and Rutile bearing assemblage represents relatively high
pressure inherited equilibrium. Image Source :
https://commons.wikimedia.org/wiki/File:Khondalite_rocks_at_Tenneti_park_
beach_Visakhapatnam.JPG

4. The rock generally contains a foliation
subparallel to lithological layering;
suggesting their sedimentary parentage.
5. Low specific gravity and pervasive
gneissic banding defined by alternate
quartzofeldspathic and ferromagnesian
mineral rich layers are also discernible.
Image Source : https://turnstone.ca/khond.htm
A Granulite Facies Metasedimentary Rock : Khondalite

Charnockite-Khondalite Series of S. India.
Locality
In the Eastern Ghats between Vijayawada and Cuttack, Bastar,
Singhbhum,etc
Economic Importance
In Singhbhum area graphite deposits are found in Khondalites, in
buildings and temples like
Sun Temple Konark and Jagganath Temple.
Image Source :
https://www.worldhistory.org/Konarak_Sun_Templ

The term was introduced by T. L Walker in 1902 to describe a garnet-sillimanite-quartz-feldspar
gneiss with or without graphite from east-central India. The rock was named after an aboriginal
tribe called “Khond”, that inhabits the Baud-Khondmals (now Phulbani) region of Orissa and Walker
was helped by them during the field work. Hence, he proposed to honor them by introducing the
term.

E C L O G I T E
1. A coarse-grained mafic (basaltic in composition) metamorphic rock.
2. Striking appearance with red to pink garnet in a green matrix of
sodium-rich pyroxene. Accessory minerals include kyanite, rutile, quartz,
lawsonite, coesite, amphibole, phengite, paragonite, zoisite, dolomite,
corundum, and, rarely, diamond. Plagioclase is not stable in eclogites..
3. Eclogite facies is determined by the temperature and pressure conditions
required to metamorphose basaltic rocks to an eclogite assemblage.
4. Diamond and coesite occur as trace constituents in some eclogites and
record particularly high pressures. Image Source : https://www.alexstrekeisen.it/english/meta/eclogite.php

Palaghat-Cauvery Suture Zone, Himalayas.
Locality
Wajrakarur Kimberlite field-Anantpur District-
Andhra Pradesh,
North Sikkim. Some parts exposed in Nagaland as well.
Economic Importance
Eclogite is the world's most dense rock of siliceous matter. It is used
for roads, abrasives, and monuments.
Image Source :
https://www.mindat.org/min-48628.html

Impressed by the beauty of the metamorphic rock from Saualpe,
Austria, René-Just Haüy (father of modern crystallography) created
the name "eclogite" (the chosen rock), which he derived from the Greek
word εκλογη (choice).
Eclogite is a rare and important rock because it is formed only by
conditions typically found in the mantle or the lowermost part of
thickened continental crust.
Eclogites are helpful in elucidating patterns and processes of plate
tectonics because many represent oceanic crust that has been
subducted to depths in excess of 35 km and then returned to the
surface.

M I G M A T I T E
1. Rock composed of a metamorphic (altered) host material that is
streaked or veined with granite rock; the name means “mixed rock.”
2. Occur on a regional scale in areas of high-grade metamorphism.
3. Forms under extreme temperature conditions during prograde
metamorphism, where partial melting occurs in pre-existing rocks.
4. Often appear as tightly, incoherently folded (ptygmatic folds)
dikelets, veins and segregations of light colored granitic composition
called leucosome, within dark colored amphibole and biotite rich
material called the melanosome.

Bundelkhand Gneissic Complex,
Chhota Nagpur Gneissic Complex.
Locality
Singrauli District-Madhya Pradesh,
Tekkali- Andhra Pradesh
Economic Importance
Migmatite is a metamorphic rock that is
primarily used for building stone, but
sometimes polished to be used for ornaments.
Image Source :
https://www.britannica.com/science/migmatite

The Finnish petrologist Jakob Sederholm first used the term in 1907 for rocks within the
Scandinavian craton in southern Finland. The term was derived from the Greek word μιγμα:
migma meaning a mixture.
Because migmatites are hybrid metamorphic-igneous rocks , they are important rocks for geologists
to study in order to better understand how rocks melt and how these melts migrate and eventually
become igneous rocks.

Because many migmatites are silica-rich, some geologists have tried
studying migmatites as a way to understand another silica-rich rocks
igneous granite. For a long time, the origin of granitic rocks was
debated by geologists. Between the 1920s and the 1960s, many
geologists argued that granites could form from sedimentary or other
non-granitic rocks through chemical alteration caused by fluids. This
theory has now been largely abandoned, and geologists now believe
that granites crystallize from melts of high-grade metamorphic rocks.
The precursors of these high-grade metamorphic rocks may be either
igneous (I-Type Granite) or sedimentary (S-Type Granite). Geologists
now understand that granitic melts can form through a variety of
melting processes. The presence of migmatites was one line of evidence
that geologists examined to determine that granites probably formed
through melting processes, not through chemical alteration processes.

G O N D I T E
1. Manganese bearing high grade metamorphic rock.
2. Composed of quartz, spessartite, rhodonite, and small percentage of
apatite. Devoid of potash feldspars.
3. These are formed by plutonic metamorphism of sediments rich in
manganese oxides.
4. The Gondites scarcely exhibit good schistosity and the minerals
generally do not have any linear arrangement.
5. Braunite, rhodonite, and other manganese silicates are often
interbanded with quartz or manganese oxides minerals. Such bands
of Gondites often exhibit small scale folds.
Image Source : https://ijisrt.com/assets/upload/files/IJISRT20JAN595.pdf

Eastern Ghats Province, Balaghat Chhindwara Region of the area of
Satpura Folding
Locality
Sundargarh Dist.- Orissa,
Balaghat region Madhya Pradesh.
Economic Importance
Source of Manganese Ore.

The manganese ores of the Manomunda-Goriajhar area belong to the Precambrian Goriajhar
Formation of the Gangpur Group in the west central part of the Sundergarh district, Orissa, India
are described as gondites (Mücke, et al., 2001).

C H A R N O C K I T E
1. A granulite facies rock; A granular hypersthene granite.
2. Commonly green in colour.
3. Origin may be igneous or metamorphic, not yet clearly defined.
4. If metamorphic origin then ,foliation or layering present i.e.,
Charnockitic Gneiss.
5. Appearance of myrmekitic quartz-feldspar growths can also be
seen. It can also be found with or without biotite, sometimes
amphibole and garnet.
Image Source : https://www.virtualmicroscope.org/content/myrmekitic-granulitecharnockite

Charnockite-Khondalite Series of S. India.
Locality
Nilgiri hills, Shveroy Hills, Thomas Mount
Chennai. In patches in Granulite belts of
Eastern Ghats.
Economic Importance
In buildings, tombs etc.
Image Source :
https://www.sandatlas.org/charnockite/

The name Charnockite was defined by Dr. T.H. Holland in 1893, in the
name of Jacob Charnock (founder of Calcutta) whose tomb is made of
this rock ( rocks quarried from a central band in the St.Thomas
Mount, Chennai) which is abundant in India.

(a) The Mausoleum of Job
Charnock at Kolkata.
(b) Inscriptions on
charnockite inside the
Mausoleum.
(c) Charnockite monument at
St. Thomas Mount, Chennai,
wherefrom the tomb stone of
Job Charnock had been
excavated
(Photo courtesy: Geological
Survey of India).
Image Source :
https://www.researchgate.net/figure/a-The-Mausoleum-of-Job-Charnock-at
-Kolkata-b-inscriptions-on-charnockite-inside-the_fig5_344031295

R E F E R E N C E S
1) G.W. Tyrrell’s book of The Principles of Petrology.
2) Atlas of Metamorphic Rocks And Their Textures by B.W.D. Yardley,
W.S. MacKenzie & C. Guilford.
3) Mindat.org (website)
4) Research Gate (website)
5) Britannica (website)
6) “Manganese Ore Mineral Hand Specimen Analysis Special Reference to
Kajalidongri Mines Meghnagar, Jhabua District, M.P “ from
International Journal of Innovative Science and Research Technology
7) Springer (website)
8) Christian.nicolet.free.fr (website)
9) Science Direct (website)
10) Geological Society of India (website)
11) Alex Strekeisen (website)
12) “The Indian Granulites” article by Indian Academy of Sciences
13) “The Granulite Facies Terrains of Southern Peninsular India”
Abstracts from Geological Survey of India.

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