Splitting Large Hard Concretions

[Doctor Mud]

Hi folks,

I'm going to be attempting to field split some large (50 cm across and greater) hard concretions.

These are Miocene siltstone concretions that contain various things including crabs and nautiloids.

I have used a mallet and chisel in the past and worked my way around the circumference.

I hear that some people use just a sledge hammer, and this lets the concretion fracture more along a natural path of weakness.

I was also thinking that for larger concs a plug and feather technique might work (http://en.wikipedia.org/wiki/Plug_and_feather)

I think that Dave Allen works with the same sort of material in the North Island in New Zealand and he uses a sledge hammer.

If you are out there Dave I'd appreciate your input too.

Thanks.

[Dave pom Allen]

a sledge hammer is the best method .once open don't forget to stabilize any loose fossil i use tin foil,i find any loose material on the concretion will generally stay in place during transit back up the hill, and don't forget to extract anything left in the counter part and take home to reconstruct. at least you only have to carry half of what you started with

[Doctor Mud]

a sledge hammer is the best method .once open don't forget to stabilize any loose fossil i use tin foil,i find any loose material on the concretion will generally stay in place during transit back up the hill, and don't forget to extract anything left in the counter part and take home to reconstruct. at least you only have to carry half of what you started with

Thanks Dave,

I'll be sure to take a sledgehammer next time. So far I've been collecting only concs up to the size of a bowling ball, with obvious signs of fossils inside. Last trip I split open a slightly larger one on the beach and got the best crab I've found so far.

There are some even larger concs that may or may not have fossils inside - but there is one way to find out!!

There tends to be large semi-spherical (< 1 m diameter) concretions and larger (> 1 m) more flattened (I guess oblate spheroid) concs. I wonder if the really big ones have anything inside??

Have you found any difference between wooden vs fiberglass shafts on the sledge hammer?

I'll post some pictures of the results.

[donnyjoe]

Have you found any difference between wooden vs fiberglass shafts on the sledge hammer?

Wood handles eventually break, especially if moisture gets under the head. The wood rots and you can't see it and the handle can break on contact or (yikes!) fly off the handle. Handles are easy to replace but that might not be convenient if your vehicle is a mile away. Fiberglass is stronger and will last for years. A miss-hit might sting your hands but won't break the handle. The exterior weathers after awhile (perhaps sun exposure) causing some glass dust or very small thin stips. This can irritate the skin of some people, like fiberglass insulation does. While working as a surveyor years ago I broke probably a dozen wood handles but never broke a fiberglass one.

[Doctor Mud]

Thanks donnyjoe,

I had a hunch that fiberglass would be the way to go - especially for hard rock.

Its funny, at the hardware store I'm looking at the sledgehammers with fiberglass handles are only $6 more expensive than the wooden ones.

The shafts on the wooden sledges are made from Hickory.

Seems worth the extra 6 bucks to me!

I had the head fly off a sledgehammer once, I don't want to repeat that!

[Doctor Mud]

Just noticed that the sledges with a fiberglass shaft have a lifetime guarantee whereas the ones with wooden shafts don't

Who wouldn't pay an extra $6 for that?

[Auspex]

Composite hammer handles have come a long way since they first appeared in the 60's, and are practically indestructible (unless you are driving wedges and frequently miss long...). The big brands generally do a better job of attaching the grip, which is now the weak point of composite hafts.

[Brian-miller]

Ok I realize this is an old thread but anyone tried using a battery hilti drill to make the hole for the plug and feather? I have found a nice ammonite sticking out of a massive concretion. (Like over 3m across) but its sticking out of the corner edge of it. Thoughts?