Preparing your fossils - a guide
From time to time, we receive a query from customers – or just members of the public – wanting advice about their fossils.
Graham e-mailed us some images of some fossils he found in a muddy quarry on Benthall Edge, Shropshire. They were still encased in the rock, and he wondered whether he could extract them for display.
We've reproduced one of Graham's images below, alongside an edited version of our reply. Hopefully it will be helpful if you have been wondering what to do with some similar fossils of your own!
Dear Graham,
The fossils you have are in a limestone, and are probably going to be
very tricky to prepare further. Limestone is made of calcium
carbonate, a mineral which is somewhat soluble, so usually the calcium
carbonate dissolves, penetrates any gaps and voids between the grains
in the rock, and cements them. This 'glues' any planes of weakness
along which the rock would be prone to split. It looks like your
rocks formed in a reef or near-shore environment, which means that the
rock doesn't have the 'layer cake' structure which is sometimes
present, because it consists of larger chunks of material (mostly
fossils and algal material). This also stops the rock splitting
easily.
In terms of preparing your fossils (i.e. extracting them from the rock), this means that you aren't going to be able to just tap the rock with a hammer and chisel and have it flake away nicely; preparation is going to be a much more delicate task. You will have to locate a very fine chisel, or ideally an engraver's tool, and delicately chip away the rock flake by flake from the surface of the fossils. (You may make some headway with a sharp knife or needle, but I have found this too laborious.) This is a big (and skilled) job which will probably take about a week's worth of evenings for each lump of rock you have. It's a fun and satisfying process, but it may be a bit more involved than you anticipated! There is an alternative which may work, but runs the risk of destroying your fossils. You could use a weak acid - lemon juice or vinegar - to dissolve away the matrix that surrounds the fossils. This may go some way to remove cemented material from the very surface of the shells, for instance; however the major problem in this case is that the acid will eat away at the fossils themselves too, because they have the same chemical composition as the surrounding rock (calcite). If you were extracting teeth or bones, which are usually preserved as phosphate, this technique would work a treat. However, in this case, you will want to experiment with this technique on some less spectacular fossils from the same area before applying it to your more treasured finds!
Regards, Martin Smith
Thanks, Graham, for letting us reproduce your query here!
GeoLogic Buyer's Guides
Feedback
We'd love to know how useful you found this page - please pop any thoughts into the form below, no matter how minor. All the fields are optional - even if you've nothing to say, do give us a rating!