Where to Split?

[Kane]

Ok, so I'm currently trying to cleave some fairly dense blue-grey shale, which generally contains some mussels, non-articulated brachs (with some very nice calcite crystals), a few nautiloids, and a lot of Eldredgeops trilobite fragments (sometimes whole ones). If there are bedding planes, they aren't obvious. This stuff is tough that doesn't break straight and clean, and there are no visible fractures to exploit.

When faced with this issue, I generally try to give some medium taps with the hammer to see if a really tiny fracture I can't see might emerge. If not, I proceed in one of two ways: 1) if I see an interesting band of fossils on the edge, I plant my chisel there, or in the absence of that; 2) I plant the chisel right in the middle so that I can continue cleaving either side in half repeatedly. Number 2 is pretty much guesswork. Sometimes I end up working the piece right down to the point that it is fat in the middle and too thin on all sides to get any splitting opportunity (mostly due to it splintering/fracturing on a diagonal rather than horizontally).

Is there a more professional way of going about this, or is it really just "how the cookie crumbles"? I've attached a pic that shows one of the slabs I've been working on. The picture doesn't do much justice to its size, and I chose to split it vertically into chunks to make it easier to work with. This is a fairly productive slab, and I'm not familiar or confident enough in working with this particular type to go whole hog on it yet.

[Fossildude19]

Looks like you are dealing with dolostone, or really hard limestone.

I usually use method 2 when dealing with rocks that don't want to break nicely. the only advice I can give to get nice fractures is to let them winter over for a few seasons. The weathering will start the process.

I would use a 3 lb crack hammer or sledge on these, and try to whack the big parts.

The good thing about material like this, is that the fossils can be just as hard, and will sometimes break nicely out of the rock. Other times,... not so much. Keep the superglue handy.

Good luck!

Regards,

[Kane]

Thanks! Just want to make sure I'm doing it right. The fossils are generally as firm as the rock, but the trilos can be a bit brittle. I'm still a novice in trying to identify the stone. I wanted to say limestone, but was unsure (my gauge in determining shale from limestone or sandstone has been the possibly unscientific guesstimation by granule size). I'd attach a few more pics, but I can't seem to in reply

[Fossildude19]

You can - just go to the lower right and select "More Reply Options", next to the "Post" button.

Shale is usually more friable,... more bedding planes visible, more easily broken. Generally speaking of course - that is, considering the layers to be more laminated. Sometimes there is cross bedding which doesn't split nicely either.

Sandstone is more identifiable by the small grains of sand/mica etc. in it.

Mudstones are a bit harder, and dolostones are really hard.

And limestones can range from soft to very hard. Kind of hard to differentiate unless you have good examples to study.

Regards,

[Kane]

Thanks again! I was just reading how to do that on the FAQ! I was thinking shale would be much more friable, but I've been wrong in the past. Just some pics from the same type of rock from last year.

[Raggedy Man]

It's nice to see I'm not the only person who takes big pieces like those back home to search. People look at me weird, but I just keep smiling...lol. I can't wait to see what you find.

Good luck!

Best regards,

Paul

[ynot]

I have had slightly better results with splitting harder rock by using lighter taps and working all the way around the edge at the same plane, multiple times. It may take longer but I have had some good results doing it this way,

Good luck!!

Tony

[Rob Russell]

It's nice to see I'm not the only person who takes big pieces like those back home to search. People look at me weird, but I just keep smiling...lol. I can't wait to see what you find.

Good luck!

Best regards,

Paul

I've considered buying truckloads of Francis Creek shale spoils, and having them dumped on a rented lot. Get about 50 yards delivered, a barbaque, and several of the gang together for some for some good times. Hahaha.

[Mike Pocock]

Looking forward to seeing what comes out.

[Mike Pocock]

Cant remember where I read it but apparently someone put a large chunk of a similar matrix in a vice and kept tightening it until it split, I suppose this would depend on how large the piece is.

Regards

Mike

[sdsnl]

It's nice to see I'm not the only person who takes big pieces like those back home to search. People look at me weird, but I just keep smiling...lol. I can't wait to see what you find.

Good luck!

Best regards,

Paul

Do you smile in a "I found lots of treasures" way or a "I'm a friendly person, don't call the cops on me" way?

[tmaier]

I agree with Ynot that tapping gently on the bedding plane edge seems to give best results. The fossil makes a flaw in the rock, and gentle tapping seems to make that flaw grow and give best exposure of the fossil. You are helping the fossil to release itself. A big whack just seems to just make new flaws, and lots of rubble.

[Fossildude19]

The issue is that the"bedding plane" is not always apparent or may not even exist in these large, less laminated blocks.

It sounds like a great technique to use if there is an obvious bedding plane.

It may also work if you are just trying to create a bedding plane in the middle of one of these blocks, by randomly selecting a layer, and tapping the chisel/hammer along an imaginary line through the block.

I will have to give this method a try.

I tend to be barbaric, and less than patient with massive bedded rocks like these, and just whack away at them with a sledge.

Regards,

[tmaier]

True that some rock you just have no clue on bedding plane, and it doesn't want to follow it even if you could identify it. If I'm removing rock fragments in situ, I start with the horizontal plane and assume in is the bedding plane. I've never used a sledge, mostly because I'm too lazy to carry something so heavy. =-) I have two type of hammers, one that has a flat chisel type end, and another that has a pointed chisel end. I use tapping with the hammer end to what I believe might be a bedding plane, and then start rotating the rock in random directions hoping a crack will be seen. Then if I see a crack form, I use the chisel to focus the blow on the crack and along that plane. The flat chisel seems best for that, the pointed chisel just seems to dig holes. If not cracks form, I give it a a couple big whacks and then declare it hopeless. =-) The nice thing about a sledge would probably be volume... you may not be very selective in where the blows are landing, but by just volume of how much is fractured, something should appear soon. If a fossil (which is normally a structural flaw in the stone) is deep in the stone, then this attempt to exploit the flaw by tapping will not work, because it just too insignificant to help you out. The fossil needs to be like 1/4 of the rock in some cases, to have a significant effect on splitting. I normally end up with wounds when I do this type of fossil hunting, and I use paper towels and masking tape as bandages. =-) I wear just sunglasses as eye protection, as long as they are plastic and not real glass. It's common to get a halo of red marks in my face around the sunglasses, from the flying chips. I haven't done that type of prospecting for many years, most Florida hunting doesn't use hammers.

[caldigger]

I just throw everything into a rock crusher and hope for the best. You mean I've been doing it wrong all this time? Darn!