"splitting" really soft slabs

[SteveE]

The other day I posted trilobite pics in this ID page thread

 

I just used a beat up drywall saw to cut the section with the trilo out of the slab, then tried to "split" the whacked at the rest of it hoping for more.   The siltstone (noncalcareous dolomite maybe?) was so soft it just crumbled.  I tried tapping around the edges, which just sort of mashed in, and also tried a chisel, which just took off crumbly flakes (and I wish that was as easy when I try to nap flint).   I knew if I found another specimen I'd destroy it trying to get at it, but went for it anyway as a technique-learning excercise.  No joy, lots of bits and pieces but no bits and pieces of trilobites    Today I collected more of what I THINK is the same material.  Before I make a mess of this too, I thought to ask you experts here..... how do you hunt fossils in slabs of really soft crumbly rock?

 

Thanks!

[connorp]

Are you asking how to extract slabs in the field or prep them once extracted?

[SteveE]

I probably posted in the wrong part of the site.... this is a "finding" question.  I have the slabs at home.   I have no idea if there are fossils hidden inside.  I've split a lot of hard rock (and cut some harder rock) but its my first try at peeking inside something that's already pretty soft.  If I try the techniques I use for harder shale and limestone, I really make a mess!  

 

[Ludwigia]

A photo of the rock might help us in advising you. Have you tried using a long-bladed pen knife?

[Ptychodus04]

Use as wide and thin chisel as possible. for Green River stuff (pretty soft) this summer we were using chisels that were around 3/32" thick and 3" wide as starters.

[Fossildude19]

PSA on Safety! 

(Be sure to use safety goggles and gloves, ... always!) 

 

I have used old butter and cake knives, putty knives, painting knives, as well as hobby knife blades, combined with a small tack hammer, with some success. 

The key at first is to use multiple blades. Once a crack begins, move the next blade along it to about 1 inch past it (leaving the first blade in the crack).

Try to place it at the same level as the starting crack. Keep using  blades, until the rock splits through.  Once you get the hang of it, you can just use one knife, and move it along the crack. 

Good luck. Keep us posted. 

[SteveE]

20 minutes ago, Ptychodus04 said:

Use as wide and thin chisel as possible. for Green River stuff (pretty soft) this summer we were using chisels that were around 3/32" thick and 3" wide as starters.

Where do you find such wide thin ones?   Mine are all for general construction and quite a bit thicker

[Ptychodus04]

Shoot me a PM. I have some thin, high carbon, steel that I can make a couple for you at a nominal cost. They are basically just a flat piece of steel (8"x3") with an edge ground on one of the ends. I can heat treat the cutting edge and temper it so it is hard but not brittle.

[SteveE]

21 hours ago, Ptychodus04 said:

... I can make a couple for you at a nominal cost.....

Thanks, though I can DIY something in my own shop.

On 11/19/2019 at 4:13 AM, Ludwigia said:

A photo of the rock might help us in advising you. Have you tried using a long-bladed pen knife?

So this started as a large slab with a visible trilobite.  The opening post has a link to the trilobite pics and they show some of the rock surface.   I have since hacked and smacked the rest of the slab, which tended to break into chunks or flake off.   Here are pics of some larger pieces of leftovers.   The junk heap has some more source material, but I'm really hoping to identify the source.  Either way, I'll try to get my hands on more stuff to practice these skills on  and hopefully find another trilobite

[Ptychodus04]

26 minutes ago, SteveE said:

Thanks, though I can DIY something in my own shop.

Make sure you get your heat treat right or your DIY chisel can shatter when you strike it... not a pleasant experience.

[SteveE]