Coal rank is based on the degree of metamorphism (coalification) and is based on heat value, fixed carbon and volatile matter in the coal. With increased rank one would expect

• A. a higher density and higher specific gravity
• B. a lower density and lower specific gravity
• C. more volatile matter
• D. less fixed carbon

Answer: (A)

As coal becomes more metamorphosed (higher rank), its composition shifts toward more fixed carbon and fewer volatiles and moisture. This change raises the calorific value and makes the coal denser, so both the density and the specific gravity increase with rank. In higher-rank coal you have more carbon-packed into the same volume and fewer light, volatile components, which drives up density. Therefore, higher density and higher specific gravity are expected as rank increases. The trends of adding more volatile matter or reducing fixed carbon don’t occur with higher rank, which is why those shifts don’t fit.