There are several supposed OOPARTs that I keep running across on these forums and others.
The problem with these supposed OOPARTs would be that most of them are fake, or at least misrepresented.
I don't have the actual gusto to chase after each and every one, here are the one I most commonly see:
Originally found in 1961 in mid-February, the Coso artifact became a object of fascination.
While searching for geodes, it's discoverer Wallace Lane, Virginia Maxey, and Mike Mikesell found the lump of stone near the dry lake bed of Owens
They took the rock back to their business, LM & V Rockhounds Gem and Gift Shop, believing it to be a geode, and cut it in half for sale.
Instead of a geode, they found a piece of ceramic covering a metals haft.
Obviously, this was surprising and caused some controversy.
Further study however showed it to be a sparkplug, specifically a 1920s Champion spark plug.
An example of a more modern sparkplug encased in conglomerate:
As objects rust, they can build up a conglomerate shell. This can include things that are near the object. I've found nails in similar conditions,
usually will happen in sandy areas. It forms a sandstone like compound, and can contain any number of objects. I've found them with glass, sticks, or
attached to buildings in the case of partially exposed foundation nails.
The klerksdorp spheres, so called because they were initially found in Ottosdal Africa and some of them are shaped like spheres.
They were featured in Forbiden Archaeology... which cited a Weekly World News article for information.
"Over the past several decades, South African miners have found hundreds of metallic spheres, at least one of which has three parallel grooves
running around its equator. The spheres are of two types--'one of solid bluish metal with white flecks, and another which is a hollow ball filled
with a white spongy center' (Jimison 1982)."
Susan Jimison was one of Weekly World News' editors.
The spheres themselves range in shape and size, from discs to semi spheres. They are pyrophyllite, basically a type of metamorphic stone.
My personal favorite is this one:
And now for my favourite OOPART:
Originally discovered in the thirties, in Khujut Rabu. They were studied by Wilhelm König, the director of the National Museum of Iraq in 1938, and
he published a paper to the possibility of them being galvanic cells, possible use for electroplating.
There are some problems with that idea, though.
Chief among them: when they tried to make them work as batteries, they had to change the structure of the artifacts.
* the bitumen completely covers the copper cylinder, electrically insulating it, so no current can be drawn without modifying the design;
* there are not any wires or conductors with them; * no widely accepted electrical equipment is associated with them. (Controversial stone
reliefs depicting arc lights have been suggested, however the voltages obtained are orders of magnitude below what would be needed to produce arc
lighting); * a bitumen seal, being thermoplastic, is excellent for forming a hermetic seal for long term storage. It would be extremely
inconvenient however for a galvanic cell, which would require frequent topping up of the electrolyte (if they were intended for extended use).
Basically, they were reworked to work as batteries, and much more strongly resemble storage vessels for sacred documents.
I'm going to take off now, seeing as how 'cause of work it took about five hours to put this together.