Yes and yes.
Nothing toxic if you use the right materials and I can make rock for less then $0.40 a pound.
For what it's worth, here is my recipe.
1 part Portland Cement
2 parts crushed coral or crushed limestone or crushed oyster shell
1 part salt (I know some people don't like using rock salt but it's always worked out for me, you just need to know you can't make rock too thin using it.)
Portland Cement is a generic term for a type of cement produced by grinding clinker into a fine powder, with a little added gypsum. There are many different types of Portland cement. The word "cement" is usually taken to mean Portland cement. When searching for cement to make your own rock, Portland Cement is not enough information.
Low alkalinity type White Portland Cement is the proper material.
Crushed oyster shell, is chock full of nitrates, phosphates, and has such a high alkalinity, the only aquarium use for it is high alkalinity tanks for African Cichlids, it is also used to feed chickens....its popularity is due to its being cheap.
Rock salt is ambiguous, and an enigma. It does nothing useful, in terms of the rock, and crystals inside the rock will not dissolve. Or seeings how water does not flow through the rock, if it does dissolve, it will dissolve very slowly.
Most folks get offended, when given the original DIY rock recipe, before it was spread via forums:
1 part White Portland Cement (low alkalinity type, Riverside suggested)
5 parts aragonite sand (seaflor special grade)
1 part acrylic shavings
Naturally porus (if mixed right)
Cures rapidly (pH stabilizes)
Inert, leaches nothing (no nitrates, phosphates or other "nasties")
