In:
Mineralogical Magazine, Mineralogical Society, Vol. 82, No. 2 ( 2018-04), p. 433-444
Abstract:
Millsite, CuTeO 3 ·2H 2 O, is a new mineral from Gråurdfjellet in Oppdal, Norway. It occurs as a minor secondary phase alongside teineite, other copper secondaries and relict primary tellurides in a boulder of quartz-rich granite, which is probably a glacial erratic. Millsite is bright cyan to royal blue in colour. The mineral is transparent to slightly translucent with a vitreous lustre and has a perfect (100) cleavage. It is brittle, has a conchoidal fracture and a pale green streak. Millsite is optically biaxial (+), α = 1.756(5), β = 1.794(5), γ = 1.925 calc and 2V meas = 60(1)°. Millsite has monoclinic space group P 2 1 / c, with a = 7.4049(2) Å, b = 7.7873(2) Å, c = 8.5217(2) Å, β = 110.203(3)°, V = 461.17(2) Å 3 and Z = 4. The empirical formula is Cu 0.99 (Te 0.98 Se 0.02 )O 3 (H 2 O) 2. The five strongest reflections in the powder X-ray diffraction pattern are [ d hkl in Å ( hkl , I rel %)]: 6.954 (100, 100), 3.558 (012, 64), 2.838 (12 $\bar 2$ , 47), 2.675 (211, 43) and 3.175 (210, 39). The crystal structure has been determined to R 1 = 0.016, wR 2 = 0.036 and GooF = 1.049. The diagnostic structural unit of millsite consists of a Cu 2 O 6 (H 2 O) 4 dimer that is decorated with four TeO 3 groups connecting adjacent dimers and defining (100) heteropolyhedral sheets. These heteropolyhedral sheets are only connected by layers of structurally significant hydrogen bonds and correlate with the (100) cleavage. Millsite is a polymorph of teineite with a unique configuration of the M 2 O 6 (H 2 O) 4 dimer that leads to a sheet topology. No isostructural selenium or tellurium analogue exists. The monoclinic polymorph ( P 2 1 / c ) of chalcomenite ‘monoclinic-CuSeO 3 · 2H 2 O’ hereafter, ahlfeldite and MgSeO 3 · 2H 2 O have M 2 O 6 (H 2 O) 4 dimers, but their configuration differs significantly from that of millsite and leads to a framework topology rather than a sheet. Teineite does not have a dimeric structure and so is fundamentally different from millsite. The sheet topology of millsite appears to be unique among tellurites.
Type of Medium:
Online Resource
ISSN:
0026-461X
,
1471-8022
DOI:
10.1180/minmag.2017.081.057
Language:
English
Publisher:
Mineralogical Society
Publication Date:
2018
detail.hit.zdb_id:
2034522-7
SSG:
13
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