As a professional geologist who spent much of his career studying basalt, I find Brown's description of this most common of all volcanic rocks lacking. For example, she writes "... minerals in the basalt, principally calcium ..." But calcium is simply one of many elements in basalt; it is not a mineral, although it can be a constituent of several different minerals. She also writes that reactions between CO2 and basalt "... convert the available elements into even more stable types of rock, such as olivine." But olivine is a mineral, not a rock, and olivine occurs naturally in almost all basalt without any human intervention.
Given its apparent lack of importance to possible sequestration, undue emphasis is given to the columnar structure present in some basalt. Moreover, while the large photo of Devils Postpile in California illustrates such columns, why not instead use a photo of one of the many highly photogenic examples of basalt columns that are abundant within the Columbia River basalt province, the very geographic focus for Brown's article? And why cite Wyoming's Devils Tower as an example of columnar basalt, when the rock of Devils Tower isn't basalt ... the rock described as possibly "the holy McGrail of carbon sequestration."
If HCN wants to educate readers about the possibilities for CO2 sequestration in basalt, pertinent facts and a tighter focus on the subject are desirable.
Valerie Brown respondsI thank Dr. Duffield for his close reading of my article. He is correct in regard to calcium; it is an element, and I regret the error in describing it. His other criticisms seem less instructive.
Dr. McGrail told me that the results of his lab experiments with basalt and CO2 are being prepared for submission to a peer-reviewed journal. I refer Dr. Duffield to the article cited in my piece, "Potential for carbon dioxide sequestration in flood basalts" by B. Peter McGrail, H. Todd Schaef, Anita M. Ho, Yi-Ju Chien, James J. Dooley, and Casie L. Davidson; Journal of Geophysical Research Vol. 111, B12202, doi:10.1029/ 2005JB004169, 2006, for an overview of the science and a statement of McGrail's hypothesis that carbonate minerals will form far more rapidly in basalt than in sedimentary formations.
With respect to the lab experiments, Dr. McGrail and his team are using a specially customized high-pressure X-ray diffraction instrument that enables them to observe the chemical reactions in real time so that they can calculate the rate at which carbonate minerals are forming. The basalt samples and the CO2 are placed in a small reactor cell and subjected to temperatures and pressures similar to those that prevail in the Grande Ronde formation of the Columbia River basalt about 3,000 feet below the surface.
Dr. Duffield is correct in saying that olivine is a mineral, but I think most people would also consider it a rock.
I admit to waxing lyrical about basalt's columnar joining. That's because it's beautiful, and High Country News deals with the beauty, as well as the structure, of the natural world.
And Dr. Duffield is correct that some sources refer to Devils Tower as phonolite, an igneous rock closely related to, and often intermixed with, basalt. But even academic geologists refer to Devils Tower as basalt occasionally. (See Growth, Dissolution and Pattern Formation in Geosystems, Bjorn Jamtveit and Paul Meakin, eds., Kluwer Academic Publishers, 1999, p. 11: "The highlight of this chapter, from a geological point of view, is an analysis of the origin of fracture patterns in columnar basalt such as the Giant's Causeway in County Antrim, Northern Ireland and the Devils Tower in Wyoming.")