Английская Википедия: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 Шаблон:Chem2,[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 Шаблон:Chem2, and Gaines et al. classify the mineral as a compound carbonate.[3] 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.[5][3]
Appearance
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.[5][4] The structure is similar to that of hydrozincite.[3] 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 Шаблон:Frac according to some sources,[6][4] but others say that the hardness is not determinable.[2][5] 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][5] 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.[5]
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.[6][5]
At the type locality it is associated with gypsum, smithsonite, pyrite and goethite.[5]
References
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