p class="MsoNormal">Archean rocks are mainly composed of two types of rocks:





A rock with a banded or leafy structure, typically coarse-grained and consisting mainly of feldspar, quartz, and mica.

The mineral composition varies from granite to gabbro.

Gneiss is the most prominent common rocks of the Archaean system. They range in composition from only slightly altered granite [igneous] or a gabbro [igneous] to a banded or leafy, true gneiss [metamorphic].
archean rock gneiss
Common minerals of Archaean gneiss are: feldspar orthoclase and plagioclase, quartz, muscovite, biotite, hornblende, magnetite, epidote and zircon.

The rocks of the Archaean system are often divided into the following three groups which are usually represented in certain regions:

i) Bengal Gneiss:

khondalite (bengal gneiss)

The highly heterogeneous Gneisses of Bengal, Bihar and Orissa and many other parts of peninsular India are include underthis group.This type of rock sometimes referred to as khondalite isactuallyeither sillimanite gneiss or sillimanite-schist.

ii) Bundelkhand Gneiss:

bundhelkhand gneiss

This group includes the large granites of Bundelkhand like Gneiss and some other areaslike BalaghatArcot and Cuddapah. The most important characteristic of these gneisses is that in hand specimens they appear as granite-leaf forms that are present on a very small scale. In many places of their occurrence, coarse-grained igneous rocks are infiltrated by mills and dams.

iii)Charnockite Series :

The range includes the vast, granite-like hypersthenes-
rich gneiss of southern India, developed extensively in Madras. In their petrological character, they are medium to coarse-grained and show mineral variation in the acid to ultra basic range, although orthopyroxene (hypersthenes) is always a significant component. 

The rock was named because of its use in the tomb of the founder of the city of Calcutta, Job Charnock.The type of rock recorded in many other parts of the world presents a challenging problem in its origin. 

It has been suggested by some that the charnockites are actually of indigenous, plutonic origin intruded into the older rocks of the Archaean group. These often occur as igneous infiltrates of dikes, lenses .but other cases also show prominent banding indicating substantial metamorphosis.

Some other typical gneisses of the Archean group of rocks, exposed in different parts and mentioned with specific names, are as follows;

Champion Gneiss:


It is exposed in Karnataka and has fine gray gneiss with good mica content. It is at the sites of intrusion in Dharwar rocks. The name is of restricted use. It is considered to be the earliest age of the Archean era.

Peninsular Gneiss:
quartz-felsper(peninsular gnesis)

It is a common gneiss rock of Archaean age occurring at various places in southern India including Karnataka. The rock couscous consists mostly of banded gneiss, with bands of quartz-felser alternating with biotite, hornblende, and other supporting minerals. Like champion gneiss, these rocks are also infiltrating the rocks of Dharwar at many places.


Schistes are abundant in Archaean rocks, they are completely crystalline and are found in many varieties such as mica-schists. Hornblende-schist etc. A coarse-grained metamorphic rock consisting of layers of different minerals and can be divided into thin irregular plates.
Contains mostly crystalline, mica, talc, hornblende, chlorite, etc.

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