Bartelkeite Explained

Bartelkeite
Category:	Germanate mineral
Formula:	PbFeGe(Ge2O7)(OH)2•H2O
Imasymbol:	Btk^[1]
Strunz:	9.J0.10 (10 ed) 4/C.08-60 (8 ed)
Dana:	7.6.2.1
System:	Monoclinic
Class:	Spheroidal (2) or prismatic (2/m)
Symmetry:	P21 or P21/m
Unit Cell:	a = 5.83, b = 13.62, c = 6.31 [Å], β = 127.31° (approximated); Z = 2
Color:	Colorless, white, very pale greenish
Habit:	tabular; acicular
Cleavage:	, distinct
Mohs:	4
Luster:	Subadamantine
Streak:	White
Diaphaneity:	Transparent
Density:	4.97
Opticalprop:	Biaxal (-)
Refractive:	nα=1.89, nβ=1.91, nγ=1.91 (approximated)
2V:	ca. 35^o (measured)
References:	^[2]

Bartelkeite is an exceptionally rare mineral, one of scarce natural germanium compounds.^[3] The formula was originally assumed to be PbFeGe₃O₈,^[4] bartelkeite was later shown to be isostructural with a high-pressure form of the mineral lawsonite. Thus, its correct formula is PbFeGe(Ge₂O₇)(OH)₂•H₂O.^[5] Bartelkeite and mathewrogersite are minerals with essential (dominant) lead, iron and germanium.^[6] Both come from Tsumeb, Namibia - a world's "capital" of germanium minerals.^[7]

Occurrence and association

Bartelkeite was detected in voids of germanium ore occurring within dolomites. The mineral associates with galena, germanite, reniérite, and tennantite.

Crystal structure

Bartelkeite is the first analyzed mineral containing both tetrahedrally- and octahedrally-coordinated germanium. It is isostructural with high-pressure form of the silicate lawsonite. In the structure there are:

• chains of FeO₆ and GeO₆ octahedra, that share edges
• Ge₂O₇ dimers that cross-link the chains
• Pb atoms and water molecules in large cavities of the framework

Notes and References

1. Warr. L.N.. 2021. IMA–CNMNC approved mineral symbols. Mineralogical Magazine. 85. 3. 291–320. 10.1180/mgm.2021.43. 2021MinM...85..291W. 235729616. free.
2. Web site: Bartelkeite - Handbook of Mineralogy . Handbookofmineralogy.org . 2016-03-12.
3. Web site: Bartelkeite: Bartelkeite mineral information and data . Mindat.org . 2016-03-04.
4. Keller, V.P., Hess, H., and Dunn, P.J., 1981. Bartelkeit, PbFe²⁺Ge₃O₈, ein neues Germanium-Mineral von Tsumeb, Namibia. Chemie der Erde 40, 201-206 (in German)
5. Origlieri, M.J., Yang, H., Downs, R.T., Posner, E.S., Domanik, K.J., and Pinch, W.P., 2012. The crystal structure of bartelkeite, with a revised chemical formula, PbFeGe^VI(Ge₂^IVO₇)(OH)₂·H₂O, isotypic with high-pressure P2₁/m lawsonite. American Mineralogist 97(10), 1812-1815
6. Web site: Mathewrogersite: Mathewrogersite mineral information and data . Mindat.org . 2016-03-04.
7. Web site: Tsumeb Mine (Tsumcorp Mine), Tsumeb, Otjikoto Region (Oshikoto), Namibia - Mindat.org . Mindat.org . 2016-03-10.