Prepping trilobites with hand tools

[connorp]

I recently acquired a nice large Olenellus trilobite. I haven't done much prepping and only use hand tools (dental pick, needles, etc), and occasionally a Dremel engraved. Most of the trilos I've prepped have been rollers from Oklahoma, and they are not too hard since they tend to be a very different color from the surrounding matrix and are not flat. I'm wondering how I should go about starting on this guy. Not sure whether its a partial not, but would like to investigate. My problem is that the trilo is nearly the same color as the surrounding matrix and very flat, making it hard to know if I've hit more fossil or not. Any tips would be appreciated.

[Douvilleiceras]

Olenellids from many Western US locations are often preserved as isolated cephalons, as is the case here. Unfortunately, there is no body on this specimen. I would advise against attempting to prep it further, as you risk damaging the rather fragile head.

[connorp]

49 minutes ago, Douvilleiceras said:

Olenellids from many Western US locations are often preserved as isolated cephalons, as is the case here. Unfortunately, there is no body on this specimen. I would advise against attempting to prep it further, as you risk damaging the rather fragile head.

Thanks for the heads up. I’ll leave it be. That said, could I still get some tips on a fossil like, assuming there was more the be prepped?

[Kane]

3 hours ago, connorp said:

Thanks for the heads up. I’ll leave it be. That said, could I still get some tips on a fossil like, assuming there was more the be prepped?

It depends on a few factors, really: hardness of the matrix versus the trilobite, its orientation in the rock, and its morphology. Understanding what the full trilobite looks like in 3D is key to knowing how much matrix to remove, as the last thing you might want to do is undercut the bug and cause breakage. That becomes a major issue with more flat bugs like these.

 

I usually begin by exploring with a pin at an approach relative to the surface matrix of 10-30 degrees. If the approach has an angle higher than that, there is a risk of gouging in too deeply and damaging what may be underneath. I then continue that probe out to where the full trilobite would end relative to the size of the piece I am seeing. From there, it is the patient process of lifting matrix on the bug with short, low angle picking, more like skimming than digging. Once you get to the axis, those are commonly rounded in many species, sloping down on either side. What I do there is use those dips as mini-leverage to pop off slightly larger bits of matrix. I know this species is pretty flat, but there is still some slight contour to it. It is just going to take a bit more patience and care than usual, so magnification is highly recommended.

 

If I was prepping an Olenellus, my angle would be very small, probably at 10 degrees, as these ones are not robust. These are not the easiest species to prep.

 

In terms of colour of a trilo being one with the matrix, I see in this picture that there appears to be a sheen on the cephalon? If so, lighting at an angle can make a difference to bring out the sheen as you prep. Sometimes I may moisten it a bit with some breath every once in a while to bring out even a minor colour juxtaposition a bit more.

[RJB]

Im with Dovilleiceras.  Appears to be only the cephalon.   Plus if you do go on the prep attack and nothing is there, then the rock will look 'not too good' with all those tool marks.  Good luck though.

 

RB

[Sagebrush Steve]

I agree this is only a cephalon, a very nice one.  I’ve got a bunch of them from a recent trip to Nevada and yours is nicer than almost all of mine.  It is difficult to do any prep work on these because the shale is very hard.  Whenever I try to do anything with dental picks or other hand tools on these I end up making it worse.