Bultfonteinite

Bultfonteinite, originally dutoitspanite, is pink to the colorless mineral with chemical formula Ca2SiO2(OH, F)4. It was named after the type locality at Bultfontein in the Free State Province of South Africa. Additional localities include in the USA, Israel, Japan, and a few others. It was discovered in 1903 or 1904 in the Bultfontein mine in South Africa, for which the mineral is named, and described in 1932.

Bultfonteinite occurs in “a large ‘horse’ of diabase and shale fragments in a kimberlite pipe” at its type locality and “in a contact zone in thermally metamorphosed limestone” at a California, USA locality. Associated minerals include calcite, apophyllite, natrolite, oyelite, scawtite, afwillite, and xonotlite.

General Information

  • Category: Nesosilicates
  • Formula: Ca2SiO2(OH, F)4
  • Crystal system: Triclinic
  • Crystal class: Pinacoidal (1) (same H-M symbol)

Properties

  • Color: Colorless, pink
  • Twinning: Interpenetrating on {100} and {010}; polysynthetic
  • Cleavage: Good on {100} and {010}
  • Fracture: Conchoidal
  • Mohs scale hardness: 4.5
  • Luster: Vitreous
  • Streak: White
  • Diaphaneity: Transparent

History

In either 1903 or 1904, a miner discovered the first specimen of bultfonteinite on the 480-foot level of the Bultfontein mine in Kimberley, South Africa. The mineral occurred in a several-hundred-foot-tall horse of kimberlite-enclosed dolerite and shale fragments. The specimen, mistakenly thought to be natrolite, was given to Alpheus F. Williams. Several years later, additional samples were found by C. E. Adams in the nearby Dutoitspan mine and given to the MacGregor Museum in Kimberley. Shortly before 1932, the mineral was found about 100 miles (160 km) to the southeast of Kimberley at the Jagersfontein Mine in Orange River Colony.

The type material is held in England at Cambridge University and the Natural History Museum in London.

Occurrence

Bultfonteinite has been found in Australia, Botswana, Canada, Israel, Japan, Jordan, Russia, South Africa, and the United States. The mineral was first located outside South Africa in the US State of California in 1955. Bultfonteinite has been found in association with afwillite, apophyllite, calcite, natrolite, oyelite, scawtite, and xonotlite.

At the type locality, the mineral occurred in a large structure of dolerite and shale fragments in a kimberlite pipe. In Crestmore, California, bultfonteinite formed in the contact zone of thermally metamorphosed limestone.

Association: Calcite, apophyllite, natrolite (Bultfontein mine, Kimberley, South Africa); afwillite, scawtite (Crestmore, California, USA); oyelite, scawtite, xonotlite (Fuka, Japan).

 

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