Scotlandite is a

sulfite Sulfites or sulphites are compounds that contain the sulfite ion (systematic name: sulfate(IV) ion), . The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive, its salts are widely used. Sulfites are ...

mineral first discovered in a mine at

Leadhills Leadhills, originally settled for the accommodation of miners, is a village in South Lanarkshire, Scotland, WSW of Elvanfoot. The population in 1901 was 835. It was originally known as Waterhead. It is the second highest village in Scotland, ...

South Lanarkshire South Lanarkshire (; ) is one of 32 unitary authorities of Scotland. It borders the south-east of the Glasgow City council area and contains some of Greater Glasgow's suburban towns, as well as many rural towns and villages. It also shares bor ...

Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...

, an area known to mineralogists and

geologist A geologist is a scientist who studies the structure, composition, and History of Earth, history of Earth. Geologists incorporate techniques from physics, chemistry, biology, mathematics, and geography to perform research in the Field research, ...

s for its wide range of different mineral species found in the veins that lie deep in the mine shafts. This specific mineral is found in the Susanna vein of

, where the crystals are formed as chisel-shaped or bladed. Scotlandite was actually the first naturally occurring

, which has the ideal chemical formula of Pb S O₃. The mineral has been approved by the Commission on New Minerals and Mineral Names, IMA, to be named scotlandite for Scotland.

Occurrence

Scotlandite is found in association with

pyromorphite Pyromorphite is a mineral species composed of lead chlorophosphate: Pb5( P O4)3 Cl, sometimes occurring in sufficient abundance to be mined as an ore of lead. Crystals are common, and have the form of a hexagonal prism terminated by the basal p ...

anglesite Anglesite is a lead sulfate mineral with the chemical formula PbSO4. It occurs as an oxidation product of primary lead sulfide ore, galena. Anglesite occurs as prismatic orthorhombic crystals and earthy masses, and is isomorphous with barite and ...

lanarkite Lanarkite is a mineral, a form of lead sulfate with formula Pb2(SO4)O. It was originally found at Leadhills in the Scottish county of Lanarkshire, hence the name. It forms white or light green, acicular monoclinic prismatic crystals, usually mi ...

leadhillite Leadhillite is a lead sulfate carbonate hydroxide mineral, often associated with anglesite. It has the formula Pb4SO4(CO3)2(OH)2. Leadhillite crystallises in the Monoclinic crystal system, monoclinic system, but develops pseudo-hexagonal forms du ...

, susannite, and

barite Baryte, barite or barytes ( or ) is a mineral consisting of barium sulfate (Ba S O4). Baryte is generally white or colorless, and is the main source of the element barium. The ''baryte group'' consists of baryte, celestine (strontium sulfate), ...

. It occurs in cavities in massive

and

, and is closely associated with

and susannite. Scotlandite represents the latest phase in the crystallization sequence of the associated lead secondary minerals. It can often be found in the vuggy

as yellowish single crystals up to 1 millimeter in length that sometimes arrange in a fan-shaped aggregates.

Anglesite Anglesite is a lead sulfate mineral with the chemical formula PbSO4. It occurs as an oxidation product of primary lead sulfide ore, galena. Anglesite occurs as prismatic orthorhombic crystals and earthy masses, and is isomorphous with barite and ...

can usually be recognized in a very thin coating on scotlandite which is used to protect the

from further oxidation. A second variety of scotlandite can also occur in discontinuously distributed cavities between the

mass containing the first variety and the

matrix. This variety is characterized by tiny, whitish to water-clear crystals, and crystal clusters less than one millimeter in size, which encrust large portions of the interior of the cavities. Scotlandite is a uniquely rare mineral, as it occurs in small amounts in few locations around the world.

Physical properties

Scotlandite is a pale yellow, greyish-white, colorless, transparent mineral with an adamantine or pearly luster. It exhibits a hardness of 2 on the Mohs hardness scale. Scotlandite occurs as chisel-shaped or bladed crystals elongated along the c-axis, with a tendency to form radiating clusters. Its crystals are characterized by the , , , , , and . faces. Scotlandite shows perfect cleavage along the plane and a less good one along the plane. The measured density is 6.37 g/cm³.

Optical properties

Scotlandite is biaxial positive, which means it will refract light along two axes. The mineral is optically biaxial positive, 2V_meas. 35° 24'(Na). The refractive indices are: α ~ 2.035, β ~ 2.040, and γ ~ 2.085 (Na). Dispersion is strong, v >> r. The extinction is β//b, and α 01= 20° (γ 00= 4° in the obtuse angle β. H(Mohs) < 2. D = 6.37 and calculated D_x = 6.40 g cm⁻³. The

infrared spectrum Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those of ...

of scotlandite shows conclusively that it is an anhydrous

, with no OH groups or other polyatomic anions being present. It is also proven by

electron microprobe An electron microprobe (EMP), also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA), is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. I ...

analysis and

infrared spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functio ...

that scotlandite must be a polymorph of lead sulfite.

Chemical properties

Scotlandite is a

compared with chemically related compounds, it is very close to the value of

(6.38 g cm₋₃), but distinctly different from that of

(6.92 g cm₋₃).

Orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic Lattice (group), lattices result from stretching a cubic crystal system, cubic lattice along two of its orthogonal pairs by two different factors, res ...

lead sulfite is of higher density (D_meas = 6.54, calculated D_x = 6.56 g cm⁻³), and has the same chemical properties as well. The empirical chemical formula for scotlandite calculated on the basis of Pb+S = 2, is Pb_l.06S_0.94O_2.94 or more ideally PbSO₃.

Chemical composition

X-ray crystallography

A small crystal of scotlandite, showing some cleavage faces, was examined using Weissenberg and precession techniques. Scotlandite is in the

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...

crystal system. The only systematic extinctions observed from the single crystal patterns were 0k0 where k was odd. Thus the possible

space group In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that ...

is either P2 or P2/m. The unit cell parameters obtained from the single crystal study were used to index the X-ray powder pattern and were then refined with the indexed powder data. A subsequent study determined the space group is ''P2₁/m'' (no. 11) with unit cell dimensions: a = 4.505 Å, b = 5.333 Å, c = 6.405 Å; β= 106.24°; Z = 2. If the present a and c axes are interchanged, the unit cell of scotlandite is very similar, isotypic, to that of molybdomenite, PbSeO₃. Lead is coordinated to nine oxygen atoms with Pb-O_av=2.75 Å, and possibly further to one sulfur atom with Pb−S=3.46 Å. The average S−O distance in the pyramidal SO₃ group is 1.52 Å.

References

{{Authority control Natural materials Lead minerals Monoclinic minerals Minerals in space group 11