Tempe Butte Stop 4 - Calcrete (Close)

You will see calcrete at the surface only where the upper part of the soil has eroded away. This takes place in washes and where people have dug up the soil. This cobble was dug up from beneath the surface.

Calcrete is principally made up of CaCO₃ or calcium (Ca) carbonate (CO₃). A good test to see if the substance is really calcium carbonate is to poor hydrochloric acid on it. The carbonate reacts when put in contact with hydrochloric acid. This video shows what happens when dilute hydrochloric acid comes in contact with the carbonate in calcrete.