Quartz after Goethite-Hematite

specimen number:
2062252

location:
Crosby, Crow Wing Co., Minnesota, USA

description:
Masses of goethite, these in the process of being replaced by hematite rich quartz. This material is often referred to by the lapidary name binghamite.

Binghamite, also known as silkstone, is a highly attractive, chatoyant variety of quartz containing fibrous inclusions of iron oxide minerals, primarily goethite and hematite, which give it a striking visual resemblance to tiger's eye. Geologically, this unique lapidary material formed within the massive Precambrian-age Biwabik Iron Formation, where complex silica-rich hydrothermal fluids slowly replaced original fibrous amphibole or iron silicate mineral structures with microcrystalline quartz, preserving the dense, parallel alignment of the oxidized iron inclusions. This perfect structural alignment triggers a beautiful, rolling cat's-eye sheen showing rich bands of red, gold, brown, and black when the material is cut and polished. Historically, binghamite was discovered in 1936 by an independent lapidarist named William Bingham in the extensive iron-mining fields of the Cuyuna Range near Crosby within Crow Wing County, Minnesota, United States. The material was primarily recovered as a scarce byproduct during large-scale open-pit quarrying and industrial iron-ore mining throughout the mid-to-late twentieth century, particularly during the peak operations of the 1940s through the 1970s. Through 2026, while the major industrial iron mines of the Cuyuna Range have long since closed and flooded, binghamite remains a highly sought-after, classic regional material for specialized collectors, with limited modern gathering restricted to independent lapidarists searching the historic mine dumps and glacial till deposits of northern Minnesota.

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