Saturday, February 16, 2013

What Does Colored Ice Have To Do With Uranium?

Nothing!  Unless you are in Iran and the ice is glowing.  The following pictures were from my son's latest experiment, Making Neat Looking Colored Ice, which he did during the blizzard.  It kept him busy for a little while as well.  The procedure was quite simple: 1) fill cups with water, 2) add a few drops of food coloring, 3) stir, 4) set outside to freeze, 5) remove from cup.  The results speak for themselves, cool looking ice structures that resemble a lava lamp that has been frozen.  BTW, these are upside down from when they were made.  NEAT!

The ice structures show some interesting features upon closer examination.  Most of the food coloring seems to have been concentrated into a ball shaped structure that has been surrounded by uncolored ice.  You can also see bubble zones in the clear ice which eventually get absorbed by a third zone of ice that mixed with food coloring.  I am not certain when this region crystallized.
I kept the geochemical jargon to a minimum.

So Why the Title?
It turns out the pure water crystallized first concentrating the food coloring into a ball which was the last region to crystallize.

What happened here also mimics what happens when when minerals (crystallize) form from a melt deep inside Earth.  As magma solidifies upon cooling, remaining melt changes composition.  The result is a pluton (solidified magma body) with regions of different composition.

Suppose a magma body containing iron (Fe), magnesium (Mg), potassium (K), uranium (U), and silcica (SiO2) solidifies, the first minerals to form will soak up most the Fe and Mg along with some silica.  Uranium is a large element that prefers to be in a melt.  When the rest of the magma finally solidifies it will have a higher concentration of K, U, and silica.  It so happens that granite represents later stage crystallization, thus is higher in U concentration when compared with most other rocks.  This was a very simplistic explanation. 

Relating this back to the Colored Ice model:  The red food coloring would represent the uranium and potassium.  The clear ice would represent the zone where crystallization of the Fe and Mg takes place.

Why Was All This On My Mind?
Someone in my son's cub scout troop was concerned about his granite counter top having radon (Rn) gas.  Since granite has a higher U concentration and Rn is daughter product of U when it decays, most anything granite does emit Rn gas.

Oh No!  Should you rip out the counter tops or sell the house?
No!  Although concentrations of Rn may be higher than background levels they are not high enough for any concern as you don't have enough granite.  Some houses, however, that have granite for bedrock should get there basements checked for radon as that is a potential hazard especially since there is minimum ventilation.

FYI - I have granite counter tops in my bathrooms.

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