Stratigraphy and Coal Geology Questions and Answers

Answer: B

The less polluting coal is Anthracite.

Anthracite is the highest rank of coal, with roughly 86-97% carbon and very little volatile matter. It burns with a short, nearly smokeless flame and gives off less soot and fewer volatile pollutants than the lower ranks.

Lignite and sub-bituminous coal are low-rank coals with high moisture and volatile content, and bituminous coal, though higher in carbon, is rich in volatile matter and burns with a smoky flame. All three release more pollutants per unit of heat than anthracite.

Answer: A

The coal described is lignite.

Lignite, or brown coal, is the lowest rank of true coal. It is brown to brownish black, keeps visible plant structure, holds a great deal of moisture and volatile matter, and has a carbon content of roughly 60-70%, so its heating value is low. India's lignite comes mainly from Neyveli in Tamil Nadu and from Gujarat and Rajasthan.

Peat has even less carbon (around 50-60%) and is not yet coal. Sub-bituminous coal is black and has more carbon and less moisture, and anthracite, the highest rank, has over 90% carbon and little volatile matter.

Answer: B

The coal described is bituminous coal, the second option.

The two words that identify it are 'banded' and 'black'. Bituminous coal is the black coal whose seams show alternating bands of bright, glossy material and dull material, and it sits above lignite and sub-bituminous coal in rank. Compared with lignite it holds much less moisture and volatile matter and much more carbon, which is what 'lower amounts of volatile, moisture and higher carbon content' compares.

Lignite is brownish-black, soft and rich in moisture, so it fails on every count. Bone coal is an impure coal carrying a large share of shale and ash, not a high-carbon one. Anthracite is the highest rank, with the least volatile matter and the most carbon, but it is a hard, uniformly lustrous coal and is not described as banded.

Read plainly, the last clause alone would point to anthracite; the official key rests on the word 'banded', which is the descriptive mark of bituminous coal, and this explanation follows the key on that reading.

Answer: C

It is called ultimate analysis.

Ultimate analysis determines the elemental composition of coal: the weight percentages of carbon, hydrogen, nitrogen, sulphur and oxygen (usually by difference). It is used for combustion calculations and for classifying coal.

Proximate analysis, the other standard coal analysis, determines moisture, volatile matter, ash and fixed carbon, not the individual elements. 'Substrate' and 'Clariviate' are not names of coal analyses.

Answer: B

This is proximate analysis.

Proximate analysis reports moisture, ash, volatile matter and fixed carbon (by difference), determined by standard heating tests. It is the routine way to assess the rank and quality of a coal.

Ultimate analysis is the elemental analysis, giving carbon, hydrogen, nitrogen, sulphur and oxygen. Thermal shock is a property of materials under sudden heating, not a coal analysis, and assay is the general word for analysing an ore, not the name of this test.

Answer: B

Coal that burns like a candle is Cannel coal.

Cannel coal is a fine-grained, dull, massive sapropelic coal rich in spores and volatile matter. It lights easily and burns with a bright, steady, smoky flame like a candle, and its name comes from an old English form of 'candle'.

Boghead coal (torbanite) is the related algal sapropelic coal, rich in oil but not the one named for the candle. Lignite is a low-rank brown coal and anthracite a high-rank coal that burns with a short, smokeless, almost flameless blue flame.

Answer: A

Gondwana coal in India is of Permo-Carboniferous age.

Almost all of India's coal, about 98% of reserves, comes from the Lower Gondwana rocks of the Damodar, Son-Mahanadi, Godavari and Satpura valleys. The main coal-bearing formations, the Karharbari, Barakar and Raniganj, are Early to Late Permian, deposited after the Late Carboniferous Talchir glaciation, which is why the age is usually given as Permo-Carboniferous.

India's younger coals are Tertiary: the Palaeogene coals and lignites of Assam, Meghalaya, Gujarat and Tamil Nadu (Neyveli lignite is Neogene). Jurassic coal is not significant in India.