Question

Which of the following is a sedimentary rock?
1. Anthracite
2. Granite
3. None
4. Quartzite

Answer 1

Correct Answer - Option 1 : Anthracite

The correct answer is Anthracite.

• Coal is a sedimentary rock usually occurring in rock strata in layers or veins called coal beds.
• Coal is a fossil fuel that forms when dead plant matter is converted into peat, which in turn is converted into lignite, bituminous, and anthracite.
• Anthracite
  • It is a high-grade coal
  • It has the highest heat content due to less amount of water present in it.
  • It is hard and dark black in colour.
  • Sedimentary Rock- Conglomerate, Shale, Limestone and Sandstone.
• Quartzite
  • It is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone.
  • Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts.

• Granite
  • Granite is hard, coarse-grained rocks of crystalline structure.
  • It is a type of igneous rocks (plutonic rocks).
  • Granites can be predominantly white, pink, or grey in colour, depending on their mineralogy.

• Sedimentary Rocks
  • The word sedimentary’ is derived from the Latin word sedimentum, which means settling.
  • Rocks (igneous, sedimentary and metamorphic) of the earth’s surface area exposed to denudational agents and are broken up into various sizes of fragments.
  • Such fragments are transported by different exogenous agencies and deposited.
  • These deposits through compaction turn into rocks. This process is called lithification.
  • In many sedimentary rocks, the layers of deposits retain their characteristics even after lithification. Hence, we see a number of layers of varying thickness in sedimentary rocks like sandstone, shale etc.
  • Depending upon the mode of formation, sedimentary rocks are classified into three major groups:
    • mechanically formed — sandstone, conglomerate, limestone, shale, loess etc. are examples;
    • organically formed — geyserite, chalk, limestone, coal etc. are some examples;
    • chemically formed — chert, limestone, halite, potash etc. are some examples.