Brianyoungite
| Brianyoungite | |
|---|---|
 Brianyoungite from Germany | |
| General | |
| Category | Carbonate mineral |
| Formula (repeating unit) | Zn3(CO3,SO4)(OH)4[1] |
| Strunz classification | 5.BF.30 (10 ed) 5/C.01-105 (8 ed) |
| Dana classification | 17.1.15 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic H-M symbol: (2/m) |
| Space group | C2/m |
| Unit cell | 15.724 Å, b = 6.256 Å, c = 5.427 Å; β = 90°; Z = 4 |
| Identification | |
| Color | White |
| Crystal habit | Rosettes of thin blades, pseudo-orthorhombic with β close to 90° [2] |
| Cleavage | Perfect on {100}, possible on {001}[2][3] |
| Mohs scale hardness | Probably 2 to 2½ |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 3.93 to 4.09 |
| Optical properties | Biaxial |
| Refractive index | nω = 1.635, nε = 1.650 |
| Birefringence | δ = 1.635[4] |
| Solubility | Readily soluble with effervescence in acids[2] |
| Other characteristics | Non-fluorescent[2] |
| References | [1][5][2][3][4][6] |
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]
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.[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 2½ 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
- ^ a b c "IMA Mineral List with Database of Mineral Properties".
- ^ a b c d e f g h i j k l m n o 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.
- ^ a b c d e f g h i "Handbook of Mineralogy" (PDF). Handbook of Mineralogy. Retrieved 2013-11-15.
- ^ a b c d e f g h "Brianyoungite: Brianyoungite mineral information and data". Mindat.org. Retrieved 2013-11-15.
- ^ a b c "Brianyoungite Mineral Data". Webmineral.com. Retrieved 2013-11-15.
- ^ a b c d Gaines et al (1997) Dana’s New Mineralogy Eighth Edition. Wiley