Are there any geologists in here?

Are the stripes in the brownish part of the rock foliation? If so, then it's a metamorphic rock, right?

Where are all the geologists hiding? Help. Help! Is there a geologist in the room?

I think the paleofag is right. Could be part of a radioralite formation. The black part is chert, the brownish stuff in between silt- or sandstone? Dont think its metamorphic.

>Could be part of a radioralite formation.

How would you explain the shape? Almost looks like someone dipped some sandstone into liquid chert.

It's not "pretty" and not an artifact/fossil - so hit it with a hammer if you want a real answer.

How would that help?

If it is radioralite, the brown part is probably the "precursor" sedimentary rock that is was formed from, right? (Forgive my naive questions, geology is not my field).

If that is so, would it be feasible to detect remains of the radiolarians with a microscope? Or would the pressure and heat have homogenized everything? How would a geologist identify this rock?

In biology, we can key organisms based on morphology and other characteristics, isn't it possible to do the same with rocks?

Radiolarite is a marine sediment, the sandstone and chert layers have their origin in changing sedimentation conditions, so the sandstone is not the precursor. The piece you have is kinda rounded, i would say its has been transported by a river after diagenesis. Just guessing tho, although i study geology im more into geophysics.

I see. So how would you explain the clear boundary between the black chert and the sandstone? If the black parts are chert, wouldn't the entire rock be chert? After all, one must assume the entire rock was exposed to similar pressures and temperature, it's only 10 cm in size.

The clear boundary between Radiolarite and Sandstone is due to a sudden change in the sedimentation process. The Radiolarite part of the stone comes from the "background sedimentation" that always happens in the area it was sedimentated. If there is a storm or slumping underwater it leads to the sandstone, which is usually sedimented in higher areas than the radiolarite, to be transported further into the sea and it will sedimentate on top of the radiolarite. After this process has happened, the background sedimentation will continue which leads to alternating layers of sandstone and radiolarite. This could be how it happend, pic related is a similar case from one of my excursions to Elba, Italy.

Very interesting!

Could the roundness of the rock be due to grinding from the ocean, a river, or perhaps a glacier? If say a vertical fragment was washed out to sea for instance, ad then somehow ended up back on land?

Also, what is the hardness of chert? Is there any tests I could do at home that would strengthen the current hypothesis that it's sandstone and chert?

Chert is quartz so hardness is around seven.