I was googling ballast today and saw an article on using masonry sand for this instead of the hobby store ballast. It warned about it possibly having iron in it but many types would work.
I wanted to see what you folks think about this?
Thank you 
Many modelers use sand as ballast. Just take a magnet to the material before placing. This should get the ferrous (iron) minerals out of it.
Chuck
I used sand as the primary ballast and ground cover on my modules. I live on a giant sand bar and work for a sand and gravel company. Washed mason sand is best. The washing process rids the sand of organic and non ferrous metals. Run a powerful magnet through it real good and dry it. It is easier to work when dry. Wetting it with your wet water can be problematic. A real fine mist is needed and thoroughly soak it real good. A mix of 1/3 glue to 2/3 water will soak in and hold it when dry. It will darken some when glued.
Pete
Yes you can use it or anything else the right size BUT. Ballast has come a long way since bird gravel or sand was the norm in the 1940’s. The color is the primary issue to be considered. Most railroads use limestone or granite and the vast majority is gray in color. Overcome that problem and you can use anything you want. Leave it sand colored and eventually you will realize something isn’t right subject to the prototype you are modeling
i have seen pictures of a few model railroads that were ballasted with sand and it looked just like what it was, sand. maybe some other modelers have used it and found a way to make it look more realistic. if so, please post some photos of your work. i would like to know your secret.
grizlump
Works, but be sure to put your magnet in a sandwich bag first or you will never get your magnet clean of all the magnetic material, and that will decrease the effectiveness of your magnet for later use.
Cleaning my magnets are easy. First thing you do is put a good set of safety glasses or goggles on and use my blow gun from the air compressor to blow the metal particles away.
Pete