Pike County, Arkansas, USA access via paved road.

The Twin Knobs One diatreme (TK1), delineated in 1981, is located 2.4 miles (3.8 km) southeast of Murfreesboro, Pike County, Arkansas and is within the northeast-trending group of pipes, plugs, and dikes that comprise the Murfreesboro district. TK1 is an elongate, bilobate pipe oriented north-south. The diatreme penetrated the Lower Cretaceous Trinity Formation, whereas the Upper Cretaceous Tokio Formation overlies portions of the pipe. These relationships suggest an emplacement age of early Late Cretaceous, which is contemporaneous with isotopic ages obtained at the Prairie Creek lamproite complex.

Rock types at TK1 include magmatic lamproites, sandy tuffs and breccias, and epiclastics. The magmatic breccias are porphyritic, with euhedral olivine, plus pyroxene and phlogopite phenocrysts set in a cryptocrystalline or glassy groundmass that also contains priderite, perovskite, and chromite. The sandy tuffs and epiclastics contain up to 30 percent quartz grains, in addition to lamproite and sedimentary rock fragments, set in a matrix of calcite, sericite, or fine-grained to cryptocrystalline glass. Diamond crystal habits include octahedra, tetrahexahedra, macles, and fragments. Megacrysts of picroilmenite, chrome spinel, clinopyroxene. orthopyroxene, garnet, and nodules of eclogite, peridotite, lherzolite. websterite, as well as crustal xenoliths, were recovered during sampling. Whole-rock and trace element geochemistry strongly suggests that Twin Knobs One has more affinities to olivine lamproite than to kimberlite.

Diamonds were discovered in Arkansas in August 1906, when a farmer named John Wesley Huddleston found a "glittering pebble" on his property. The next year the New York Times described "Diamond John's" treasure in epic terms: "The story of the discovery of diamond fields in one of the poorest counties of the not over-rich State of Arkansas reads like a chapter of Sinbad's adventures."

A lot of funny business has gone on around the Arkansas diamond field over the past century. After failing to gain full control of the area in 1910, the London-based Diamond Syndicate allegedly set up a sham operation to downplay the mine's potential and sabotage production, according to a Justice Department investigation. In 1919, two rival processing plants burned to the ground on the same January night, fueling rumors that someone was out to destroy the mine's profitability. In the late 1920s, Henry Ford was set to buy Arkansas industrial diamonds for his assembly lines, but the Diamond Syndicate and De Beers bribed the mine's owner to keep it out of commission.

Ford’s interest in Arkansas diamonds was based on the fact that they lasted longer in the industrial grinding and polishing processes than diamonds from other countries.
Shenanigans continued into the 1950s, when, for instance, an entrepreneur trucked some gravel from the diamond field to his own five acres north of town and plunked down a sign claiming he had a diamond mine. Locals found him beaten up in a ditch the next morning, according to a story one Arkansas geologist has told over the years.

The Twin Knobs One property has been owned by the same family since before the discovery of diamonds.