Tarbuttite
Tarbuttite from Broken Hill mine (Kabwe mine) in Central Province, Zambia
General
Category	Phosphate minerals
Formula	Zn2(PO4)(OH)
IMA symbol	Tbt[1]
Strunz classification	8.BB.35
Dana classification	41.6.7.1
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
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[2]
Identification
Color	White, colorless, yellow, red, green, or brown
Crystal habit	Equant to short prismatic [001], sheaf-like aggregates, crusts, individual crystals rounded and deeply striated
Cleavage	Perfect on {010}
Fracture	Irregular, uneven
Mohs scale hardness	3.5
Luster	Vitreous, pearly on cleavages[2]
Streak	White
Diaphaneity	Transparent, translucent
Specific gravity	4.12; 4.19 (calc.)
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,[3] strong[2]
Ultraviolet fluorescence	Non-fluorescent[4]
References	[3]

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 Coventry Tarbutt.

Tarbuttite is white, yellow, red, green, brown, or colorless; in transmitted light it is colorless.^[3] 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.^[5]

The mineral occurs as equant to short prismatic crystals up to 2 cm (0.79 in), in sheaf-like or saddle-shaped aggregates, or as crusts.^[2] Individual crystals are commonly rounded and striated.^[3]

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).^[6]

Tarbuttite was discovered in 1907 in Broken Hill mine, Northern Rhodesia, (now Kabwe, Zambia).^[3][7] The mineral was described from specimens in cellular limonite in the largest hill of the group, Kopje No. 2.^[8][9] In a cave discovered in Kopje No. 1 by boring a tunnel,^[7] tarbuttite was also found in association with hopeite as obscure crystals and crystals smaller than 1⁄16 mm (0.0025 in)^[9] and as an encrustation on some bones.^[10] Several specimens of the mineral were collected by Percy Coventry Tarbutt, a director of the Broken Hill Exploration Company.^[5][8] In 1907, the name tarbuttite was proposed by L.J. Spencer in the journal Nature in honor of Tarbutt.^[5]

When the International Mineralogical Association was founded, tarbuttite was grandfathered as a valid mineral species.^[3]

Tarbuttite has been found in Algeria, Angola, Australia, Canada, China, Namibia, the United States, and Zambia.^[2][3]

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.^[2]

• List of minerals named after people

• Cocco, G.; Fanfani, L.; Zanazzi, P. F. (1966). "The crystal structure of tarbuttite, Zn2(ОH)РО4" (PDF). Zeitschrift für Kristallographie. 123 (5): 321–329. doi:10.1524/zkri.1966.123.16.321. S2CID 96221726.
• Palache, P.; Berman H.; Frondel, C. (1960). "Dana's System of Mineralogy, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc. (Seventh Edition)" John Wiley and Sons, Inc., New York, pp. 869–871.
• Spencer, L. J. (April 1908). "On Hopeite and other zinc phosphates and associated minerals from the Broken Hill mines, North-Western Rhodesia" (PDF). Mineralogical Magazine. 15 (68). The Mineralogical Society: 1–38. Bibcode:1908MinM...15....1S. doi:10.1180/minmag.1908.015.68.02. Archived from the original (PDF) on 2014-01-06. Retrieved 2012-07-14.

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

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