| Brianyoungite | |
|---|---|
 Brianyoungite from Germany | |
| General | |
| Category | Carbonate mineral |
| Formula | Zn3(CO3,SO4)(OH)4[1] |
| IMA symbol | Byo[2] |
| Strunz classification | 5.BF.30 (10 ed) 5/C.01-105 (8 ed) |
| Dana classification | 17.1.15 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (sameH-M symbol) |
| 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°[3] |
| Cleavage | Perfect on {100}, possible on {001}[3][4] |
| Mohs scale hardness | 2 to 2.5 |
| 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[5] |
| Solubility | Readily soluble with effervescence in acids[3] |
| Other characteristics | Non-fluorescent[3] |
| References | [1][6][3][4][5][7] |
Brianyoungite is asecondaryzinccarbonate mineral. The Commission on New Minerals, Nomenclature and Classification (CNMNC) of theInternational Mineralogical Association (IMA) classifies it as acarbonate with the formulaZn3(CO3)(OH)4,[1] butsulfate groups SO4 also occupy the carbonate CO3 positions, in the ratio of about one sulfate to three carbonates,[3] so other sources give the formula asZn3(CO3,SO4)(OH)4, and Gaines et al. classify the mineral as a compound carbonate.[7] It is similar in appearance tohydrozincite, another zinc carbonate.[5] It was discovered in 1991 and designated IMA1991-053.[5] In 1993 it was named "brianyoungite" after Brian Young (born 1947), a field geologist with theBritish Geological Survey, who provided the first specimens.[4][7]
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 bcrystal axis, and tapering to a sharp point.[3] The crystals are white and transparent to translucent, with a vitreouslustre and a whitestreak.
The mineral belongs in theorthorhombic crystal system, or themonoclinic with β (the angle between the a and c crystal axes) close to 90o.[3] Thespace group is unknown, but assumed to be either P21/m, P21 or P2221.[4][5] The structure is similar to that ofhydrozincite.[7] There are four formula units perunit cell (Z = 4) and the lengths of the sides of the unit cell are a = 15.724Å, b = 6.256 Å and c = 5.427 Å.[3]
Brianyoungite is a soft mineral withMohs hardness similar tohalite, only 2 to2+1⁄2 according to some sources,[6][5] but others say that the hardness is not determinable.[3][4] It is fairly dense, withspecific gravity 3.93 to 4.09, similar to that ofcelestine.Cleavage is perfect perpendicular to the a crystal axis (perfect on {100}) and possible perpendicular to the c crystal axis (possible on {001}).[3][4] It is readily soluble with effervescence in acids.[3]
The mineral isbiaxial, withrefractive indices nω = 1.635 and nε = 1.650 and maximumbirefringence δ = 1.635.[5] It exhibitsstraight extinction.[3] It is not fluorescent.[3]
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.[5] The type material is conserved at theRoyal Museum of Scotland, Edinburgh, Scotland, 1992.17.1–8.[4]
Brianyoungite occurs withgypsum on rubblylimestone in theoxidised zone of Brownley Hill Mine, and on specimens from the nearby Smallcleugh mine.[3] It may be a secondary post-mining mineral.[6][4]At the type locality it is associated withgypsum,smithsonite,pyrite andgoethite.[4]