Calcium Carbonate

Calcium Carbonate is found almost everywhere on earth.  It can form naturally inoganically or rocks (especially Calcite and Limestone).  As well as it forms organically in Shells (Sea and Egg). It can even be found in leafy green vegetables. 
You may have it around the house, as it can be used to settle an upset stomach.  Because it is an alkali it will counteract too much stomach acid.

Under Candian Hazard Regulations this product is recognized as not hazardous.

Check out a MSDS for Calcium Corbonate from VWR