More than two years ago the writer made an x-ray examination of greenalite from the iron formation of the Mesabi Range in Minnesota. It was noticed that the powder of greenalite gave a definite pattern on which that of quartz was superimposed. The pattern did not resemble chlorite (or thüringite which is definitely a chlorite), nor biotite, nor glauconite or stilpnomelane. Neither was any resemblance observed between greenalite and chamosite, which gives a pattern different from any mentioned above. About a year ago the writer, when investigating serpentine, noticed a striking similarity in the powder photographs of it and greenalite. About this time Jolliffe1 published a paper containing microscopic and chemical data on greenalite with which the present findings could not be reconciled.