At the northeast corner of the big pipe lay a six-acre tract differing considerably from its expansive counterpart to the south. Much of this area, especially the west side, consisted of dense hardebank, a weather-resistant form of peridotite that would require both “the immediate use of drilling and explosives to extract in any considerable quantity” and the purchase of expensive crushers for further processing. Still, a black-gumbo surface layer appearing almost identical to that on the big slope extended throughout most of the east half and part of the remainder.
 Fuller to Loree, June 25, 1908, in “Reports and Information,” 19, 13 (the spelling of the word varied: hardbank, hardebank, or hardibank). Fuller referred to Mauney’s “about six acres” and recommended against acquiring it because it was “mostly composed of Hardibank . . ..” Woodford provided more detail about the dark surface layer and the hardebank, and concluded, “This hard rock cannot be worked” (Report to Ozark Corporation, October 28, 1908, 4).
Also see John W. Bishop’s statement about the Millars’ evaluation of the Mauney Mine in 1912: Deposition, John W. Bishop, in Bettie L. Mauney, et al. v. Austin Q. Millar, et al., 1920, Arkansas Supreme Court 6029 (the deposition was reprinted fully as “The Origin and History of the Mining Lease Entered into Between M.M. Mauney and Bettie L. Mauney, His Wife, and Howard A. Millar and Associates,” Pike County Courier, July 18, 1919, p. 1). The Nashville lawyer emphasized that the northeast slope was “a difficult proposition” because “hardibank boulders occupied largely the area and in the language of Howard Millar, it appears that there was a ‘horse’ in the center of the tract and probably after testing out the loose disintegrate surrounding this apex of rock or hardibank that it would probably become necessary to sink a shaft and . . ..” Defending the Millars in a law suit, Bishop of course exaggerated the difficulty of testing.
Today, a visitor to Crater of Diamonds State Park can stand on the high ridge separating the two slopes and easily see the difference in materials.
 Woodford, ibid.; infra, Millars; John R. Reigart, Mining Engineer, Ford Motor Company, and Charles W. Cook, Geologist, University of Michigan, to the Ford Motor Company, Reports on the Ozark Diamond Mine, September 10, 1923 (Reigart) and September 7, 1923, Accession No. 60, Box 1, “Diamonds–Arkansas,” Benson Ford Research Center, The Henry Ford Museum, Dearborn, Michigan. Reigart and Cook studied the northeast slope, including the Mauney Mine, as a team after Austin Millar drew Ford’s attention to the pipe as a possible source of industrial diamonds. Both submitted reports, but Cook deferred to Reigart on most matters. The latter’s analysis of the six acres was easily the best produced during the era. Reigart and Cook included complementary maps of the hardebank (intrusive peridotite), volcanic breccia, and sandstone composing the slope.