Crystallization of sugar solution, and oddly crunchy candy with fudge-like texture after eating I've been trying to recreate the results from:
http://cookingsciencetradition.blogspot.com/2010/12/crystallization-of-sugar.html

to very little success.

My process:

1: Add 1 + 1/2 cups white refined sugar, and an arbitrary amount of water to a pot.

2: Add some heat, and stir until sugar fully dissolved

3: Allow sugar to boil (without stirring) on high heat until 240F is reached

4: Turn off heat, and allow to cool until 100F is reached

5: Pour into mixer, and beat.




What goes wrong:

While the sugar is cooling, it seems to crystallize on the surface.
Then, during the beating process, it beats without turning into crumble, going from a clear syrup to a white almost crystalline looking substance (with visible strands within the substance resembling the etching seen in ribbon candy), but after only 40 seconds of beating, it starts to give the electric mixer trouble -- first starting to spew strands of candy at the sides of the mixing bowl, and then turning to crumble (identical, visually, to the crumble which is shown in the link I gave above) if left mixing too long. If I stop the mixing right when it starts spewing strands of candy, then it quickly hardens into a strange mass, almost identical to a very hard icing -- Hard, and visibly rough, fragile and crumbling when pressure is applied (though not turning to dust!), quickly melting/dissolving in the mouth into a very smooth, creamy feeling substance (not dissimilar to what fudge does in the mouth!) when consumed.

To be honest, I have no idea what is going on, or why my candy is behaving this way. Is there something obvious here that I am doing wrong? Is it possible that what is happening is actually exactly what should be happening? The reason I doubt this, is that the website I linked shows a picture of the result when the sugar syrup is cooled and beaten properly -- though my product has exactly the same color, it does not have the glossy shine which is showcased in the link's photo.

Now, it is possible that my thermometer is not calibrated correctly -- for the sake of faster problem solving, let's assume that my thermometer is of godly quality (though, I am still open to human error being the cause -- IE, maybe I misread the temperature during the cool-down process, and this is why it turned to crumble?)

Miscellaneous facts:
I live at 96.343 m above sea level.
Indoor humidity is typically around 53%. Outdoor humidity can be as high as 70%-80%.
I use filtered water




Questions summarized:

Am I making any obvious mistakes?
Does the ratio of water to sugar matter? I would think not, since the ratio between sugar and water is dependent upon the boiling point, and hence temperature of the mixture.
Is my altitude screwing things up? Could that cause problems with my (momentarily ungodly) thermometer?
Does humidity have anything at all to do with this?
Is anything even going wrong to begin with -- could it be that I am crazy, and what I describe is exactly what ought to happen?

Thank you very much for your time, and potential answers! I hope I can eventually get this right.
It looks like you are trying to make sugar fondant.  I often make a batch to use as seed crystals in my holiday fudge preparation.

Sugar Fondant

Sugar fondant is a crystalline sugar confection where the crystals are microscopic and suspended in a saturated solution of sugar.  Its texture is very short, and the mouth-feel is creamy.

Creating sugar fondant is relatively easy. In brief, boil a syrup to softball stage and cool it undisturbed until around 50C followed by rapid agitation until the fondant is too difficult to work.

Now for some specifics.

Multiphase Solutions

One of the interesting features of boiling syrups is the temperature is intrinsically linked to the composition of the syrup.  Unlike how boiling water transitions to steam at a constant temperature of  100C, syrups boil at a range of 110C to well over 200C.  As water evaporates from the boiling syrup, the composition changes to contain a higher concentration of sugar and the boiling temperature rises.

Be warned.  You are boiling a super-saturated solution.  Any crystallized sugar introduced to the solution will not dissolve and it will seed crystallization during the cooling stages.  


Avoid stirring once the sugar has fully dissolved prior to boiling.  Use a brush moistened with hot water to wipe away any crystallized sugar on the side of the pot during cooking.  
If you are adding any glucose to the syrup, add it after the syrup has come to boil to ensure that the other sugars have fully dissolved.


Candy Stages

The desired properties of a candy are principally derived from the candy stage to which you cook your syrup.  The sugars remain mostly unchanged chemically (though disaccharides may break down into glucose and fructose) regardless of the candy stage or temperature.

When making sugar fondant, you are aiming for the softball stage which is 110C to 120C.  You can take a dollop of hot syrup and drop it into cold water to check the stage in absence of a good thermometer or if altitude / humidity are affecting your candy.  So long as you do not scorch the sugar, you can add water and lower the temperature to restore the syrup to the desired candy stage.

Crystallization

The most important part of a sugar fondant is the formation of microscopic crystals.  The syrup must cool to 50C before agitation to create the desired crystal size and distribution.  

One difficulty that I have found is that I cannot let the syrup cool within the bowl of my stand mixer - the syrup cools unevenly which typically induces crystal growth.  This is especially difficult for fondant, as it must be worked for a significant amount of time to crystallize.

Depending on your desired purpose for the fondant, you may let the syrup cool to a lower temperature or agitate less to keep the texture longer or more pliable.  If you agitate at a higher temperature, the syrup will form crystals that grow tremendously during agitation and make the fondant grainy or crunchy.

But Why Is It Crunchy?

Chances are, you have undissolved sugar in the syrup.  


Be sure all of the sugar dissolves before you add any glucose to your syrup. 
Don't stir once it begins to boil.


Your syrup might be at a higher candy stage.  If you somehow managed to reach soft crack or hard crack, this might prevent the syrup from forming any crystals and resulting in an amorphous sugar glass.