Lahnsteinite is a basic sulfate mineral first discovered in the Friedrichssegen Mine, Germany in a

goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the "α" polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...

cavity. Though found in goethite, the crystals of Lahnsteinite are few millimeters in size, and are tabular shaped. Lahnsteinite was the first mineral discovered in the Lahn Valley deposits. The empirical formula for lahnsteinite is (Zn_3.3,Fe_0.27,Cu_0.11)_3.91(S_0.98O₄)(OH)₅*3H_2.10O.

Occurrence

Lahnsteinite was first found in a cavernous kidney-like goethite. Typically Lahnsteinite is found near goethite, pyromorphite, quartz and native copper. When found with these minerals, the Lahnsteinite crystals are overgrowing the walls of several cavities. Lahnsteinite is a uniquely rare mineral, as it occurs in very small amounts in two known locations around the world. The first location is in the mine it was found in, just outside of Lahnstein Germany, the second, in a small mine in southern California.

Physical properties

Lahnsteinite is a colorless or lightly blue colored transparent mineral. It exhibits a hardness of 1.5 on the

Mohs hardness scale The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...

placing it right between talc and gypsum. This is characterized by the perfect mica-like cleavages planes parallel to the face. Lahnsteinite crystals occur as hexagonal plates combining to form a triclinic cell. The major forms are and

faces The face is the front of an animal's head that features the eyes, nose and mouth, and through which animals express many of their emotions. The face is crucial for human identity, and damage such as scarring or developmental deformities may affe ...

. Lahnsteinite is flexible with lamellae cleavages. The measured density is 2.98 g/cm³.

Optical properties

Lahnsteinite is biaxial negative, no dispersion of optical axes was observed.

Chemical properties

The chemical composition of lahnsteinite was determined on a Tescan Vega II XMU SEM equipped with an INCAx-sight EDS that operates on a tungsten cathode at an accelerating voltage of 20 kV. The current of the absorbed electrons on Co was 0.6 nA. The angle of selection of X-ray radiation was 35°, and the focal distance between sample and detector was 25 mm. The F, Na, Mg, Al, P, Cl, K, Ca, Mn, As, Sb, Pb, and Bi contents in lahnsteinite are below their detection limits by electron microprobe. The water content was measured with gas chromatography of the product of the ignition of the mineral at 1200 °C.

Chemical composition

X-ray crystallography

The X-ray powder diffraction pattern of Lahnsteinite is readily indexed in a triclinic unit cell with the unit-cell dimensions refined by the least squares method a = 8.35(3), b = 14.48(4), c = 18.60(6) Å, α = 89.4(2), β = 90.2(1), γ = 90.6(2)°, V = 2249(8) Å3. The single-crystal X-ray diffraction data were collected with an Xcalibur CCD diffractometer, MoKα radiation. The triclinic (space group P1) unit-cell dimensions calculated from the single-crystal data are a = 8.3125(6), b = 14.545(1), c = 18.504(2) Å, α = 89.71(1), β = 90.05(1), γ = 90.13(1)°, V = 2237.2(3) Å3, Z = 8

References

{{Authority control Hydrates Sulfate minerals Zinc minerals Triclinic minerals Minerals in space group 2