Details

Autor(en) / Beteiligte

• Lei, Zhilan
• Chen, Xinghai
• Wang, Jianxiong
• Huang, Yingchun
• Du, Fangfang
• Yan, Zier

Titel

Guite, the spinel-structured Co 2+ Co 3+ 2 O 4 , a new mineral from the Sicomines copper–cobalt mine, Democratic Republic of Congo

Ist Teil von

• Mineralogical magazine, 2022-04, Vol.86 (2), p.346-353

Erscheinungsjahr

2022

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Abstract Guite (IMA2017-080), Co 3 O 4 , is a new mineral species and an important economic mineral found in the Sicomines copper-cobalt mine, located ~11 km southwest of Kolwezi City, Democratic Republic of Congo. The mineral occurs as a granular agglomerate, 50 to 500 μm in size, and is associated closely with heterogenite in a quartz matrix. Guite is opaque, has a dark grey colour with metallic lustre and a black streak. In reflected light microscopy, it is white with no internal reflections. The reflectance values (in air, R in %) are: 27.0 (470 nm); 25.6 (546 nm); 25.2 (589 nm), and 24.6 (650 nm). The average of 20 electron-microprobe analyses is Co 71.53, Cu 0.58, Mn 0.67, Si 0.25, O 26.78, total 99.82 wt.%, corresponding to the empirical formula calculated on the basis of 4 O apfu: (Co 2+ 0.92 Cu 2+ 0.02 Si 4+ 0.02 ) Σ0.96 (Co 3+ 1.98 Mn 3+ 0.03 ) Σ2.01 O 4.00 , with Co 2+ and Co 3+ partitioned using charge balance. The ideal formula is Co 2+ Co 3+ 2 O 4 . Guite is cubic with space group Fd $\bar{3}$ m . The unit cell parameters refined from the single crystal X-ray diffraction data are: a = 8.0898(1) Å, V = 529.436(11) Å 3 and Z = 8. The calculated density of guite is 6.003 g/cm 3 . The eight strongest observed powder X-ray diffraction lines [ d in Å ( I/I0 ) ( hkl )] are: 4.6714 (16.7) (111), 2.8620 (18.4) (220), 2.4399 (100) (311), 2.3348 (10.4) (222), 2.0230 (24.8) (400), 1.5556 (26.3) (511, 333), 1.4296 (37.7) (440) and 1.0524 (10.1) (731, 553). The crystal structure of guite was determined by single-crystal X-ray diffraction and refined to R = 0.0132 for 3748 (69 unique) reflections. Guite has a typical spinel-type structure with Co 2+ in tetrahedral coordination with a Co 2+ –O bonding length of 1.941(1) Å, and Co 3+ in octahedral coordination with a Co 3+ –O bonding length of 1.919(1) Å. The structure is composed of cross-linked framework of chains of Co 3+ –O 6 octahedra sharing the equilateral triangle edges (2.550 Å) in three directions [0 1 1], [1 1 0], [1 0 1] with Co 2+ filling the tetrahedral interstices among the chains. Guite is named in honour of Prof. Xiangping Gu (1964–).