The outside world doesn’t know a lot of about the formulas being used by Calera, the secretive company that wants to make cement out of seawater and carbon dioxide, but now know that it has nothing to do with microbes.

Speaking at the Green is Gold event in San Jose, Calif. on Wednesday, Khosla Ventures’ Alex Kinnier said that the process does not involve microorganisms. Earlier in the year, some sources indicated that plankton or other microbes might be crucial to the process: coral, after all, metabolically transform minerals, nutrients and gases into massive reefs. Founder Brent Constantz is also an expert in biomineralization. (Disclosure: This was also a theory I had advocated.)

Without a biological agent, however, the controversy between Constantz and Ken Caldeira, a well-regarded and notable climate scientist with the Department of Global Ecology at the Carnegie Institution of Washington, will continue until even more details emerge.  Caldeira has examined the public documents that Calera has released and argued that they do not appear to reduce carbon dioxide.

Caldeira has said that Calera may just be taking calcium carbonate, the principal ingredient in cement, putting it through chemical reactions with other materials like magnesium hydroxide to get magnesium oxide, calcium and carbon dioxide. The company then likely remixes to get calcium carbonate.

"They are just putting back what they started out with," he said in April. "I think all they are doing is taking alkaline minerals and returning them back to be carbonate materials."

Calera has strongly denied and refuted Caldeira’s claims. It has also pointed out that it is producing batches of cement at a prototype factory in Moss Landing, California. Still, has not trotted out its formulas in detail.

Even if Calera can make cement, the company will then face an uphill climb in testing and validation. Contractors and architects – who have to build structures that last for decades – are notoriously conservative. Thus, it might appear in sidewalks long before it shows up in buildings. Zeobond, an Australian green cement company with a process from the 1940s, is taking this approach.

Kinnier did not break from that tradition. He said that Constantz originally approached Khosla by stating that he had been studying how Egyptians made cement.

“The Egyptians didn’t have furnaces that we have to create cement, but its structure seems to be holding up pretty well,” said Kinnier.

Kinnier then added: "I can take CO2 – and I don’t have to separate out CO – and put that through sea water and sprinkle some pixie dust, and I can get calcium carbonate and magnesium carbonate out of that." By his math, you can make a ton of cement and emit no CO2. It’s moving to market.

In an earlier patent application, Calera did not identify its pixie dust by name, but it did outline some of the things it might be working on. See the full application here. One section reads:

"[0049]In normal sea water 93% of the dissolved CO.sub.2 is in the form of bicarbonate ions (HCO.sub.3.sup.-) and 6% is in the form of carbonate ions (CO.sub.3.sup.-2). When calcium carbonate precipitates from normal sea water, CO.sub.2 is released. Above pH 10.33, greater than 90% of the carbonate is in the form of carbonate ion, and no CO.sub.2 is released during the precipitation of calcium carbonate. While the pH of the water employed in methods may range from 5 to 14 during a given precipitation process, in certain embodiments the pH is raised to alkaline levels in order to drive the precipitation of carbonate compounds, as well as other compounds, e.g., hydroxide compounds, as desired. In certain of these embodiments, the pH is raised to a level which minimizes if not eliminates CO.sub.2 production during precipitation, causing dissolved CO.sub.2, e.g., in the form of carbonate and bicarbonate, to be trapped in the carbonate compound precipitate. In these embodiments, the pH may be raised to 10 or higher, such as 11 or higher."