Tarbuttite

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Tarbuttite
Tarbuttite.JPG
Tarbuttite from Broken Hill Mine (Kabwe Mine) in Central Province, Zambia
General
Category Phosphate minerals
Formula
(repeating unit)
Zn2(PO4)(OH)
Strunz classification 8.BB.35
Dana classification 41.6.7.1
Crystal symmetry Pinacoidal
H-M symbol: 1
Space group: P1
Unit cell a = 5.400 Å, b = 5.654 Å
c = 6.465 Å, α = 102.51°
β = 102.46°, γ = 86.50°
Z = 2[1]
Identification
Color White, colorless, yellow, red, green, or brown
Crystal system Triclinic
Cleavage Perfect on {010}
Fracture Irregular, uneven
Mohs scale hardness 3.5
Luster Vitreous, pearly on cleavages[1]
Streak White
Diaphaneity Transparent, translucent
Density 4.12 g/cm3 (measured)
Optical properties Biaxial (-)
Refractive index nα = 1.660
nβ = 1.705
nγ = 1.713
Birefringence δ = 0.053
2V angle 50° (measured)
Dispersion Weak,[2] strong[1]
Ultraviolet fluorescence Non-fluorescent[3]
References [2]

Tarbuttite is a rare phosphate mineral with formula Zn2(PO4)(OH). It was discovered in 1907 in what is now Zambia and named for Percy Tarbutt.

Description and habit[edit]

Tarbuttite is white, yellow, red, green, brown, or colorless; in transmitted light it is colorless.[2] Traces of copper cause green coloring, while iron hydroxides cause the other colors. Colorless crystals tend to be transparent while colored specimens have varying degrees of transparency.[4]

The mineral occurs as equant to short prismatic crystals up to 2 centimetres (0.79 in), in sheaf-like or saddle-shaped aggregates, or as crusts.[1] Individual crystals are commonly rounded and striated.[2]

Structure[edit]

Zinc ions are surrounded by oxygen in a nearly perfect trigonal bipyramid and phosphate groups are tetrahedral. The crystal structure consists of zig-zag chains of Zn1 polyhedra linked by phosphate groups and pairs of Zn2 polyhedra. In each unit cell are two formula units of Zn2(PO4)(OH).[5]

History[edit]

Tarbuttite was discovered in 1907 in Broken Hill, Northern Rhodesia, (now Kabwe, Zambia).[2][6] The mineral was described from specimens in cellular limonite in the largest hill of the group, Kopje No. 2.[7][8] In a cave discovered in Kopje No. 1 by boring a tunnel,[6] tarbuttite was also found in association with hopeite as obscure crystals and crystals smaller than 116 mm (0.0025 in)[8] and as an encrustation on some bones.[9] Several specimens of the mineral were collected by Percy Coventry Tarbutt, a director of the Broken Hill Exploration Company.[4][7] In 1907, the name tarbuttite was proposed by L.J. Spencer in the journal Nature in honor of Tarbutt.[4]

When the International Mineralogical Association was founded, tarbuttite was grandfathered as a valid mineral species.[2]

Occurrence[edit]

Tarbuttite has been found in Algeria, Angola, Australia, Canada, China, Namibia, the United States, and Zambia.[1][2]

Tarbuttite forms as secondary mineral in oxidized zinc deposits. It has been found in association with cerussite, descloizite, hemimorphite, hopeite, hydrozincite, "limonite", parahopeite, pyromorphite, scholzite, smithsonite, and vanadinite.[1]

References[edit]

  1. ^ a b c d e f "Tarbuttite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved July 13, 2012. 
  2. ^ a b c d e f g "Tarbuttite". Mindat. Retrieved July 13, 2012. 
  3. ^ "Tarbuttite". Webmineral. Retrieved July 13, 2012. 
  4. ^ a b c Spencer, p. 22.
  5. ^ Cocco, p. 321.
  6. ^ a b Spencer, p. 1.
  7. ^ a b Spencer, p. 2.
  8. ^ a b Spencer, p. 30.
  9. ^ Spencer, p. 31.

Bibliography[edit]

Further reading[edit]

  • Richmond, Wallace E. (December 1938). "Tarbuttite" (PDF). American Mineralogist (Mineralogical Society of America) 23 (12): 881–893. 

External links[edit]

Media related to Tarbuttite at Wikimedia Commons