Calcium sand is 99.9% calcium carbonate, and is coloured with natural vegetable extracts to create great colours for your vivarium. Because it is so pure, it is easy digestible by your reptile unless swallowed in large quantities. If your reptile regularly does this, it may become impacted and require veterinary treatment. The risk is low providing you use a feeding bowl, but if you reptile is a messy eater there are other options:
You can keep your reptile on an Exo Terra Sand Mat: This is a great invention that gets rid of the danger of ingesting large quantities of sand - it's all attached to the mat, and will feel like sand on your reptiles feet of belly, but can't find its way into your reptile's tummy.
There are also a great selection of completely natural sands to be grabbed a lot prices, including riverbed sand and desert bedding.