Questions About Fossil Preservation...

[Wakaritai]

Many of the fossils I find, especially the corals, are geodized, agatized, or have some other mineral deposit "coatings".

Also, many of those don't have consistent "coating" of these minerals on the outside. They seem "faded," or whitish, where the other parts are clear or colorful. I'm guessing it is because one size was exposed to the elements, and the other parts remain protected.

So, is it actually exposure that causes these changes? If so, what are the main culprits? Drying out? Sun damage? How long does it take for these changes to take place? Is the damage permanent, or can it be repaired somehow?

Are these fossils in danger of further deterioration if kept in doors? Are there any steps that need to be taken to protect them?

Some examples...

First, a fresh, colorful agatized bryozoan (at least I think that's what it is) that I'd like to maintain. Second is the "good side" of a small piece of agatized coral. Notice the reflections and clear mineral deposits, though it is a bit dirty, with black spots... The third pic is the same specimen from the second pic, but the "bad side." Notice the "matted," white mineral deposits, and how much it varies from the second pic. The last pic is of the same specimen, but it has a combination of areas of different preservation (oxidation?) levels.

[Auspex]

This fairly simple question entails a huge range of answers, and the specifics probably need to be addressed on a case-by-case basis.

Fundamental variables include:

>Type of preservation (cast/mold, replacement, secondary pseudomorph...

>The minerals involved in the above.

>The geologic and meteorologic forces inflicted on the specimen.

>A mix of some or all of the above!

Fortunately, specimens from a given site often share similar "makeup", and thus similar methods of conservation, so the learning process might best be pursued by that category.