In which type of fossil, both the external as well as internal structure are preserved?

Option 1 : Petrification

The correct answer is Petrifaction.

Concept:

• Fossilization is defined as the physical, chemical and biological processes that lead to the preservation of plant and animal remains over time.
• Some common methods of fossilization are petrifaction, permineralization, compression, casts and molds.

• Petrifaction is the process by which biological material transforms into a fossil by replacing the original material and filling the original pore spaces with minerals.
• The fossils formed as a result of this process typically contain a significant amount of the original material of the specimen. 
• Groundwater containing dissolved minerals fills the pore spaces and cavities of specimens, most notably bone, shell, or wood. 
• When these minerals precipitate out of the water, they fill the pores of the organisms tissues.
• These are the best, but most rare, types of fossils because they preserve both the external forms and the internal structures.
• The cellular details are preserved due to the infiltration of minerals like MgCO₃, CaCO₃, SiO₂, FeS, etc. into the tissue.

• Pseudofossils: 
  • Inorganic rocks that appear to be fossils are sometimes mineral deposition.
• Compression:
  • Plant parts such as leaves, stems, and seeds are compressed by the sediments' vertical pressure.
  • Flattened plant parts are retained as thin carbonaceous films and the outline of external features.
  • Internal structures are generally not preserved.
• Incrustation:
  • The deposition of carbonate minerals and iron occurs in the form of a hard cast or incrustation around the plant parts.