Silicate based sand is bad to use in your tank. Aragonite based sand is what you want, so if you are looking for a mix buy a bag ov live sand and mix it with some regular sand for the aquarium and you should be fine.
some play sand is safe, southdown for example was and is a safe choice. However you would be hard pressed to find it since the company has since changed the name to castle sand. that was sold at Home Depot. look at the label and go to the website and check its contents.
By the way don't go by the "not for aquarium use" printing, since most play sand will have that printed on the label. Thats how they keep you from buying all the playsand for your tank at $3 a bag as opposed to $25. Just make sure its not a silicate based sand like previously stated.