[seeker32]

I had some CaCl2 lying around and it hydrated itself into a liquid. So I poured it out onto my concrete patio and tried burning some magnesium ribbon in the puddle.
It burned with a very bright red flame and left weird feathery tentacle like residue where the magnesium burned. Does anyone know exactly what occurred? I know calcium burns red, but I wasn't expecting the magnesium to ignite the calcium chloride. And what is the chemical formula of that odd residue?

[Arkcon]

You had a solution of Ca²⁺ salt in the presence of a very hot flame -- that is the definition of a flame test.  Most people use cheaper fuel sources, say a natural gas flame, but the impressive thermal energy of burning magnesium is a good way to excite ions to generate their emission spectrum.  I often see the magnesium ribbon ash to be white and feathery after burning.

[MrTeo]

And what is the chemical formula of that odd residue?

I often see the magnesium ribbon ash to be white and feathery after burning.

MgO