Brianyoungite

Brianyoungite is a secondary zinc carbonate mineral. The Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA) classifies it as a carbonate with the formula Zn3(CO3)(OH)4,[1] but sulfate groups SO4 also occupy the carbonate CO3 positions, in the ratio of about one sulfate to three carbonates,[2] so other sources give the formula as Zn3(CO3,SO4)(OH)4, and Gaines et al. classify the mineral as a compound carbonate.[6] It is similar in appearance to hydrozincite, another zinc carbonate.[4] It was discovered in 1991 and designated IMA1991-053.[4] In 1993 it was named "brianyoungite" after Brian Young (born 1947), a field geologist with the British Geological Survey, who provided the first specimens.[3][6]

Brianyoungite
Brianyoungite from Germany
General
CategoryCarbonate mineral
Formula
(repeating unit)		Zn3(CO3,SO4)(OH)4[1]
Strunz classification5.BF.30 (10 ed)
5/C.01-105 (8 ed)
Dana classification17.1.15
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/m
Unit cell15.724 Å,
b = 6.256 Å,
c = 5.427 Å; β = 90°; Z = 4
Identification
ColorWhite
Crystal habitRosettes of thin blades, pseudo-orthorhombic with β close to 90° [2]
CleavagePerfect on {100}, possible on {001}[2][3]
Mohs scale hardness2 to 2.5
LusterVitreous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity3.93 to 4.09
Optical propertiesBiaxial
Refractive indexnω = 1.635, nε = 1.650
Birefringenceδ = 1.635[4]
SolubilityReadily soluble with effervescence in acids[2]
Other characteristicsNon-fluorescent[2]
References[1][5][2][3][4][6]

Appearance
Brianyoungite (white) with fluorite and sphalerite from the Brownley Hill Mine, Cumbria, England.

The mineral occurs as tiny rosettes less than 100 µm across, composed of thin blades just one or two micrometers across, elongated parallel to the b crystal axis, and tapering to a sharp point.[2] The crystals are white and transparent to translucent, with a vitreous lustre and a white streak.

Structure

The mineral belongs in the orthorhombic crystal system, or the monoclinic with β (the angle between the a and c crystal axes) close to 90o.[2] The space group is unknown, but assumed to be either P21/m, P21 or P2221.[3][4] The structure is similar to that of hydrozincite.[6] There are four formula units per unit cell (Z = 4) and the lengths of the sides of the unit cell are a = 15.724 Å, b = 6.256 Å and c = 5.427 Å.[2]

Physical properties

Brianyoungite is a soft mineral with Mohs hardness similar to halite, only 2 to ​2 1⁄2 according to some sources,[5][4] but others say that the hardness is not determinable.[2][3] It is fairly dense, with specific gravity 3.93 to 4.09, similar to that of celestine. Cleavage is perfect perpendicular to the a crystal axis (perfect on {100}) and possible perpendicular to the c crystal axis (possible on {001}).[2][3] It is readily soluble with effervescence in acids.[2]

Optical properties

The mineral is biaxial, with refractive indices nω = 1.635 and nε = 1.650 and maximum birefringence δ = 1.635.[4] It exhibits straight extinction.[2] It is not fluorescent.[2]

Occurrence

The type locality is the Bloomsberry Horse level of the Brownley Hill mine, Nenthead, Alston Moor District, North Pennines, North and Western Region (Cumberland), Cumbria, England.[4] The type material is conserved at the Royal Museum of Scotland, Edinburgh, Scotland, 1992.17.1–8.[3]
Brianyoungite occurs with gypsum on rubbly limestone in the oxidised zone of Brownley Hill Mine, and on specimens from the nearby Smallcleugh mine.[2] It may be a secondary post-mining mineral.[5][3] At the type locality it is associated with gypsum, smithsonite, pyrite and goethite.[3]

References
  1. "IMA Mineral List with Database of Mineral Properties".
  2. Livingstone, A.; Champness, P.E. (1993). "Brianyoungite, a New Mineral Related to Hydrozincite, from the North of England Orefield" (PDF). Mineralogical Magazine. 57 (389): 665–670. doi:10.1180/minmag.1993.057.389.10. ISSN 0026-461X.
  3. "Handbook of Mineralogy" (PDF). Handbook of Mineralogy. Retrieved 2013-11-15.
  4. "Brianyoungite: Brianyoungite mineral information and data". Mindat.org. Retrieved 2013-11-15.
  5. "Brianyoungite Mineral Data". Webmineral.com. Retrieved 2013-11-15.
  6. Gaines et al (1997) Dana’s New Mineralogy Eighth Edition. Wiley
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