Rock Fudge

[bugdba]

I am helping my daugher with her science project. We are simulating the rock cycle with the creation of a fudge rock. Her question is how does the cooling rate effect the crystal size in igneous rocks. The hypothesis is if I let my fudge rock cool at room temp (73 degress F), then the rock will have larger crystals than cooling at 35 degrees F (frig) and 0 degress F (freezer). The recipe requires the mixing of evaporated milk (silt), sugar (quartz crystals), margarine (organic sediment), marchmallows (limestone pieces), nuts (sandstone pieces), chocolate chips (basalt pieces) and vanilla extract (crude oil). The ingredients are basically mixed together melted and then cooled to form an igneous rock. However, I am not sure we can prove the hypothesis with this experiment. I would expect the sugar to dissolve within the mixture and will not be visible. Is there another way to do this or can the question and hypothesis be worded differently to work with this experiment?

[paulsdecarli]

I agree; the fudge is a poor simulation of an igneous rock. For one thing, the components (nuts marshmallows, etc.) don't melt to form a homogeneous liquid. However, you may be stuck with the experiment.

As a contract researcher, I can recall doing experiments I was sure wouldn't work. The final report became an exercise in diplomatically explaining to the client why his (almost always a him) pet project was not successful.

The story board for the fudge project might be to explain how real igneous rocks differ from fudge.

[bugdba]

Thanks for the response. Yes, I think we are stuck with the experiment since the project is due in a couple of weeks. I like your idea about the story board and will probably use it. Thanks again.

[deleted-71447]

I had a geology professor who loved to use food analogies for rocks. Brownies & fudge were his favorite points of reference for metamorphic rocks. In both cases, changes occur as the materials are heated and water is driven out. As Paul and you mentioned, that is not a good analogy for igneous rocks, which form by mineral precipitation from a homogeneous liquid during cooling.
If you must use fudge, then you might be able to score some extra points by discussing results in the context of metamorphic rather than igneous processes. If you must stick with igneous processes, you could try something like freezing solutions of alum or sugar at different rates by insulating one container and leaving one open in the freezer, or in a container of dry ice. I think that would be a decent analogy for igneous formation for a K-5 project, and I think it would be doable within a couple of weeks.
Won't be as yummy as fudge though.
Good luck!
Chris

[bugdba]

Thanks Chris. I like the alum or sugar solution idea for the igneous rock. If I use sugar would the procedure include boiling water to dissolve the sugar before freezing? I don't think sugar fully dissolves in regular tap water. Please advise.

[deleted-71447]

Hi Bugdba,
Yes, that's what I was thinking - boil some water and dissolve as much sugar (or salt, or alum) as possible, then cool it down. You
Come to think of it, we already have a project description for something very similar using maple syrup:
https://www.sciencebuddies.org/science- ... p044.shtml
Chris

[bugdba]

Thanks Chris,

We are doing a variation of the experiment you provided. We are using sugar and water and then cooling in the freezer in insulated and uninsulated cups. Also, we used food coloring to distinguish between mixture cooled in the different cups. Crystals appear to be formed which look like shards of broken glass. I assume these are the actual crystals? How exactly am I supposed to measure them to determine size? They look like connected pieces of triangular pieces of glass. Any insight would be appreciated.

[deleted-71447]

Hi Bugba,
It sounds like you are getting some interesting results. It seems reasonable to assume that the separate "shards" are different crystals. Are they forming mostly at the surface of the water? Did you notice any obvious differences in the shapes or sizes of the crystals between the different cups?

For measurements, there are many ways to do it and I'm not sure what would be best. If you see crystal faces at the surface of the water, you could count the total number of crystals at the surface of the water, and divide by the area of the surface (using the equation for a circle's area?) to come up with an average area. If there are too many to count at the surface, you could draw a line at random across the surface and count the number of crystals intersected by a line of a certain length.

There are lots of other ways to approach this, and these are just a few suggestions. Whatever you do, it's always good to take lots of photos with some common object (e.g. a penny or ruler) for scale.

Chris