Arkansite

Arkansite—a mineral that exists in ten U.S. states and eleven countries—is actually brookite, the rarest of the three polymorphs (minerals containing the same chemistry but different internal structures) of titanium oxide. All three polymorphs—brookite, rutile, and anatase—are found at Magnet Cove (Hot Spring County). The brookite crystals found at Magnet Cove are sharp, black, and lustrous as opposed to the transparent or translucent brown/black crystals found elsewhere. This results from the substitution of varying amounts of iron and niobium for titanium in the structure.

Charles Shepard (1804–1886) laid claim to the discovery of arkansite in a report he published in 1846. He named the “new” mineral arkansite after the state where the specimen he examined had been found. When a new mineral is discovered, scientists worldwide seek specimens to study.

In 1849, an editor of Philosophical Magazine published a note from W. H. Miller stating that the arkansite of Magnet Cove was crystallographically identical to brookite. Researching separately, four additional scientists also published reports in 1849 stating that the composition was the same. The reports of these scientists—J. D. Whitney, Teschemacher, C. Rammelsberg, and Damour Des Cloizeau—were obscure but nevertheless documented.

The scientific community and mineral collectors took notice when J. Francis Williams published the “Annual Report of the Geological Survey of Arkansas for 1890.” He confirmed that arkansite is actually brookite. Since that time, knowledgeable collectors label specimens as brookite. Some old specimens continue to be mislabeled as arkansite. Currently, if arkansite is listed in any mineral publication, it refers the reader to brookite for information.

Because of the rarity of brookite, specimens are highly prized by mineral collectors, but this mineral has little commercial value.

For additional information:
Charles Upham Shepard Papers. Smithsonian Institution Archives, Washington DC.

Holbrook, Drew F. “A Brookite Deposit in Hot Spring County, Arkansas.” Little Rock: Arkansas Resources and Development Commission, 1947.

Howard, Michael J. “Brookite, Rutile Paramorphs after Brookite, and Rutile Twins from Magnet Cove, Arkansas.” Rocks & Minerals 74 (March/April 1999): 92–102. Online at https://www.tandfonline.com/doi/abs/10.1080/00357529909602522 (accessed August 31, 2023).

Roberts, Willard L., Thomas J. Campbell, George R. Rapp, and Wendell E. Wilson, eds. Encyclopedia of Minerals. 2nd ed. New York: Van Nostrand Reinhold, 1990.

Helen Pennington
Pine Bluff, Arkansas