Collecting and Processing
'Orsten' fossils are phosphatized – this is a fluor apatite, similar to our tooth material. Therefore, such fossil can be obtained from limestone rock but dissolving the surrounding limestone away using diluted acetic acid. The entire process is illustrated on the right side for the method developed for Orsten material from Sweden. Klaus has described general aspects in several papers, which are summarized here. Material from differenet areas may require adaptation to specific differences.
There are two major difficulties with regard to successing in yielding Orsten-type fossils: 1) the discovery of suitable rock in the field and 2) the picking and sorting quality. Many underestimate particularly the latter aspect, which requires a very good microscope and skills in recognizing the specimens – and organiszed working. Sloppy documentation, for example, is a catastrophy.
1) Discovery: Recognition of phosphatized fossils on or in the rock in the field is impossible due to their size. The only exception are the shields of phosphatocopines, which may be discovered on some of the nodules. Klaus had found them and this was one of the characteristics of a rock to select and etch it. Another aspects are the colour and the size of the crystallites. The numerous calcified Agnostus-pisiformis shields are, however, no indicator, although Klaus and his assistants had uncovered more than a hundred phosphatized young stages of it. For example, Dieter once collected 'Orsten' nodules from a road cut, but all were just "empty".
Another thing we known know is that limestones having yielded 'Orsten'-type fossils are not necessarily nodular like those from Sweden. The material from Siberia is not nodular but layered, more crust-like.
2) Processing: After some cleaning from recent dirt and contamination, the rock is crunched to pieces and out into a sieve with a mesh size of about 200µm mesh size. Another one with a mesh size of 100 or 50 µm is put underneath. These are placed in a 10-l bucket and covered with water containing 10% acetic acid. Buffering may be done, but is not really necessary due to the amount of calcium. After about 10-14 days, the residues are rinsed and dried and put into bottles.
3) Selecting: The sorting process under a microscope is time-comsuming and should be done very carefully by skilled persons. People not trained in differentiated viewing will not find much under the microscope. Again, Klaus Müller has selected very special, handmade ZEISS microscopes for this, which he stil thinks are not only the very best, but only instruments to yield the 'Orsten' material.
The fossil fragments are spread into a flat rectangular bowl with a grid on the surface and sorted out using a fine brush. Each wanted fossil is swept into a Franke cell, which is placed underneath the sorting plate in a kind of carrier, which has a hole in the center. The unwanted rest can be stored in a corner. Grid quare by grid square is searched through and emptied until the surface is clean except the corner with the remains. These are put into a second bottle. Slowly, the original residue bottle is emptied and and portion by portion looked through. Eventually the remains are put back into the numbered residue bottle.
The next step is a detailed check of the Franke cells for 3D fossils rather than small shellies and conodonts (if they haven't remained in the remains already). Both these elements are also phosphatized and interesting, but were not the direct scope of our 'Orsten' research. The material may also contain other phosphatized fossils such as brachiopod shells and also sponge spicules (secondarily changed into phosphate or primarily silicified).
At this light microscopy stage of processing the material, we cannot identify if fossils are well preserved. They are not only tiny, but shiny and appear to look nice. Details cannot be seen very well. Yet, as you may see from the image on the right side, there the ventral details body and limbs are ill-preserved, and only the soft membrane, inner lamella, that spans between out shield rim and body appears nice. Therefore, investigations are restricted, therefore, to scanning electron microscopy – "our eye", so to speak.