What Chemicals or Minerals turn to rock when you add water?

Question

I was up in the Sierra mountains and found some fine white powder, (it seems like sand) and when I added water and kneaded it turned to rock. Why did it do that? What Mineral would cause it to turn to rock?

Answer 1

its on the periodic chart....

i cant think of the element right now

but it starts with the letter "P"

Answer 2

could this be a spill,

I can't think of any thing naturally occuring that would not have already turned to rock by previous rain fall.

so if it could be a spill it likely could be:

plaster of paris (CaSO4)2 dot H2O which with water forms gypsum CaSO4dot2H2O

quick lime :CaO which can form solid Ca(OH)2 &/or Ca(OH)2dotH2O

slaked lime: Ca(OH)2  which can form Ca(OH)2dotH2O

and then there are like portland cement

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with all that said, this is my best quess,  because of the location & description:

& finally there is "liquid dynamite'"  which is mixed with water , & poured into holed drilled in rocks (it expands & cracks open the rock... a favorite of trail crew in the back country wilderness where other means of trail maintainence is not allowed to remove  large rock.

There are several similar products including Bristar and Betonamit. There is a web page which explains the process http://www.demolitiontechnologies.com