Bill, sent us this question....
As fossils come from many different strata and therefore comprise of different minerals to some others. In which part of the world would you find the 'best' ones with regards to ease of extraction and robustness (if those don't go together). What do you do with fragile ones?
As you rightly say, fossils are found in a great range of rock types. These rock types reflect the environments in which the fossils lived. For example, many dinosaur fossils are found in rocks that formed in coast and river plains, near where the dinosaurs lived, and where their bones could be easily buried and fossilised after the animal died.
As to where the 'best' fossils are found, it depends what you mean by 'best'. Some of the best-preserved fossils are found in rocks deposited in the deep-sea, for example the arthropods of the famous 'Burgess Shale'. Many complete, pristine fossils of insects and plants are found in ancient lake deposits, which also occasionally (and extremely rarely) preserve dinosaurs, pterosaurs, fish and frogs with 'soft tissues' preserved. These are the remains of the soft muscles and skin of the animals, which, in exceptional circumstances may be preserved along with the bones. These fossils are extremely rare and valuable. The photo is of an insect from the famous Messel group in Germany (about 40 million years old). It even preserves the original colour and irridesence of the beetle's body.
Most fossils are represented only by the bones and shells of the animal. How robust these fossils are depends largely on how well mineralised the remains are, and on how much disturbance the rock layers have been exposed to. Fragile bones can be hardened with glues and resins before being encased in plaster for extraction. There are many kinds of glues now available and fragile bones often require extensive work to support them. Sadly some still degenerate over time (especially those collected and repaired in the 1800s) and fossils are lost when they crumble away to nothing. Darren Naish reported on this situation in dinosaurs very recently in his blog here.