Fluor-liddicoatite

Fluor-liddicoatite is a rare member of the tourmaline group of minerals and elbaite subgroup. It forms a series with elbaite and probably also with olenite. The color is usually smoky brown, but also pink, red, green, blue, or rarely white. Formulae are-

  • Fluor-liddicoatite Ca(Li2Al)Al6(BO3)3Si6O18(OH)3F
  • Elbaite Na(Al5Li1.5)Al6(BO3)3Si6O18(OH)4
  • Olenite NaAl9B3Si6O27O3(OH)

Fluor-liddicoatite was named in 1977 after Richard T. Liddicoat (1918–2002) gemmologist and president of the Gemological Institute of America, who is well known for introducing the GIA diamond grading system in 1953.

General Information

  • Category: Cyclosilicate (Tourmaline Group)
  • Formula: Ca(Li2Al)Al6(BO3)3Si6O18(OH)3F
  • Crystal system: Trigonal
  • Crystal class: Ditrigonal pyramidal (3m) (same H-M symbol)

Fig: Fluor-liddicoatite (tourmaline group)

Properties

The streak is white to very light brown, lighter than the mass color, luster is vitreous and crystals are transparent to translucent. The mineral is brittle, with an uneven to conchoidal fracture. It is very hard, with hardness 7.5, a little harder than zircon, making it suitable for use as a gemstone. Specific gravity is 3.02, a little lighter than fluorite. It is neither fluorescent nor radioactive.

  • Formula mass: 945.8 g/mol
  • Color: Usually smoky brown, but also pink, red, green, blue, or rarely white.
  • Crystal habit: Stout prismatic, with a curved convex trigonal outline
  • Fracture: Uneven to conchoidal
  • Tenacity: Brittle
  • Mohs scale hardness: 7.5
  • Luster: Vitreous
  • Streak: White to very light brown
  • Diaphaneity: Transparent to translucent
  • Specific gravity: 3.02

Occurrence

The type locality is Anjanabonoina, Tsilaizina, Antsirabe, Madagascar. Type Material is stored at the National Museum of Natural History, Smithsonian Institution, Washington, D.C., US, catalogue #135815; further type material is stored at the Natural History Museum, London, the Royal Ontario Museum, Canada and the Geological Survey of Canada.

 

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