Calera, Inc. discovers a way to capture carbon dioxide emissions at a California power plant and use them to make cement.

Calera, Inc. discovers a way to capture carbon dioxide emissions at a California power plant and use them to make cement. This is a win for the power company, which needs to reduce its carbon dioxide emissions, and a win for Calera. Calera decides to patent this invention. What kind of patent would this be? A machine? A composition of matter? A manufacture?