absorption time for sedimentary rock

[deleted-45846]

My son is doing the "Rocky Secrets: Where Does Oil Hide?" project for his 5th grade science project. He dropped 5 drops of mineral oil on a 15 gram shale rock and we are 8 hours in to "total absorption". Should it be totally dried up, with just the darker color left, or can there still be a little puddling on the certain parts of the rock? We have no idea what the "absorption" bench mark should be. Can anyone give us any guidance on what the expected wait time should be? A ballpark figure according to weight of the rock?

Thank you.

[kgudger]

Hello and welcome to the forums!

I looked at the experiment, and while I think the instruction "Stop the stopwatch when the oil has soaked into the limestone" is somewhat ambiguous, I would think that "soaked into" merely means when there is no liquid on the surface. In other words, when the rock surface no longer has any liquid sitting on top of it. If you feel that 5 drops are too many to start with, you could start the experiment with 1,2,3,4 drops instead.

I will also ask other experts to comment on your question.
Keith

[deleted-45846]

Thank you so much for the reply! That definitely helps. My son put the 5 drops on the shale samples and it literally took 15, 10 and 8 hours for the oil to soak in. I didn't think that the experiment was intended to take so long, but this is our first time in doing something like this. Please let me know if you find anything else out. THanks!

[deleted-71588]

I don't know what your piece of shale looks like. Look at the picture in http://en.wikipedia.org/wiki/Shale. Shale is a sedimentary rock that is layed down in layers. Some layers have a high concentration of quartz. If you are testing oil absorption time by putting the drop on the top of a quartz layer, then I'm not surprised it is taking a very long time.

Try putting the drop on an edge where you can see the layers of mud between layers of quarz and calcite.

You can think about this like a piece of wood. The tree moved liquids up and down easily in tube like structures so a cut that crosses these tubes (called end grain) will absorb stain much faster than any smooth cut that doesn't cross these tubes. The same is true of shale.

[deleted-45846]

The experiment is called: Rocky Secrets: Where Does Oil Hide? Question: "which sedimentary rock is the best storage rock for oil?"

We have finished watching and timing the rocks in this experiment and there are no clear winners. Shale held the most oil, but sandstone absorbed faster. Should we only pay attention to how much oil the rock sample held, and if so, why did the experiment ask to time absorption rate, or does absorption time play into this as well? We have done some background research on the rocks and have learned that it depends on the actual surface of the rock (surface of, crevices, holes), so it may just be our samples. Would this be an acceptable result, if it just depends on the rock samples the experimenter was given for the experiment, or would it need to be a broader answer about shale, limestone or sandstone. I guess my question is: is there a correct answer when it come to these three types of sedimentary rocks?

Thank you.