Metamorphic changes in rocks are primarily result of three main factors that are also sometimes called agents of metamorphism: heat, pressure and chemically active fluids.

Traces of bedding planes may be found as relict structures in some slates. The slaty cleavage is result of severe type of dynamic metamorphism of clays and shales.

Anthracite is considered highest grade coal with fixed carbon ranging between 92-98 percent. It has highest calorific value in coals and burns without any smoke, as volume matter is negligible.

The correct answer is Coal.

Key Points

• Gondwana rocks contain nearly 98% of India’s coal reserves.
• The carbon content is very low.
• The Gondwana rock system is also called  Carboniferous rock system.
• They are deposits ordered down in synclinal troughs on ancient tableland surfaces.
• Gondwana System or Carboniferous period System or Dravidian System is major coal deposit of India. 

• The Gondwana rock system is named after Gond people, found in Madhya Pradesh, Odisha, etc.
• The deposits were laid down in synclinal troughs on ancient plateau surface.
• The rock system was formed 250 million years ago.
• Iron ore, copper, uranium, etc are also found here. 
• Rajasthan was leading producing state accounting for (21%) of total production of limestone, followed by Madhya Pradesh & Andhra Pradesh (11% each).
• Asia's only active diamond mine is situated in Majhagaon about 55km away from Khajuraho in Madhya Pradesh.
• It is located in interior of  Panna district.
• The mine is spread over an area of 80km belt, starting from Paharikhera North-East to Majhgawan South-West with a breadth of around 30 km.
• The major copper mines are Khetri copper belt in Rajasthan, Singhbhum copper belt in Jharkhand, and Malanjkhand copper belt in Madhya Pradesh which are mined by HCL.
• Singhbhum belt is mined by M/s Indian Copper Complex.

Coal may broadly be defined as metamorphosed sedimentary rocks of carbonaceous character in which raw material has mostly been supplied by plants of various groups.

Foliation generally results due to rmodynamic metamorphism in coarse-grained igneous rocks like granites and sandstones and metamorphic rocks like schists.

The correct answer is Archaean Rock

Key Points

• Archaean Rock
• Age of Formation: These rocks are oldest, dating back to around 4 billion years ago when molten magma cooled and solidified in upper crust of earth's surface.
• Characteristics:
  • ?Azoic (lacking fossils)
  • Crystalline (due to volcanic origin)
  • Foliated (composed of thin sheets)
  • Highly deformed and faulted
  • Often formed as plutonic intrusions (volcanic rocks found deep inside)
• Primary Rocks:
  • Gneiss: These rocks cover two-thirds of peninsular India and have varying mineral compositions from granite to gabbro, with foliated or banded structures.
  • Schists: These rocks are predominantly crystalline.
• Locations:
  • Himalayas
  • Central and sourn parts of Peninsula
  • Orissa, Meghalaya, Madhya Pradesh, Chhattisgarh, and Chotanagpur Plateau of Jharkhand
  • Bundelkhand
• Importance:
  • These rocks contain mineral resources such as mica, talc, hornblende, chlorite, etc.

Additional Information

• Dharwar Rock 
  • The Dharwar rock system is named after rocks discovered and studied in Dharwar district of Karnataka, where y are abundant. These rocks were formed and deposited in three major cycles, dating back from 3,100 million years ago to 1,000 million years ago.
  • Characteristics:
  • They are oldest metamorphosed sedimentary rock system in world, resulting from metamorphosis of sediments of Archaean gneisses and schists.
  • Primary Rocks:
  • Hornblende, Schists, Quartzites, Phyllites, Slates, Crystalline Limestones, and Dolomites.
  • Location: Found in Dharwar-Bellary-Mysore belt of Karnataka, as well as in Jharkhand, Madhya Pradesh, Chhattisgarh, Odisha, and Himalayan region.
  • Importance: These rocks are economically significant due to ir valuable minerals such as high-grade iron-ore, manganese, copper, lead, and gold.

The rock with schistose structure is made up of broadly parallel or sub-parallel layers or bands of flaky, platy or rod-like minerals making it very weak in direction of parallelism.

Residual shales are formed from decay and decomposition of pre-existing rocks followed by compaction and consolidation of particles in adjoining basins without much mixing.

Since biotite is metamorphosed to form biotite-schist, colour is not changed much and hence colour of biotite-schist is also black.