Blue spinel crystals in the MgAl2O4-CoAl2O4 series: Part I. Flux growth and chemical characterization
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Veronica D’Ippolito
,
Ferdinando Bosi
Abstract
Natural blue Co-bearing spinel crystals are rare and actively sought as gemstones, while synthetic blue Co-bearing spinel powders are largely used as ceramic pigments. High-quality spinel single crystals with compositions closely corresponding to the solid-solution series spinel sensu stricto (MgAl2O4)-cobalt spinel (CoAl2O4) were produced by flux growth method, with Na2B4O7 as flux. Lowcooling rates (2 °C/h) and linear temperature profiles were applied in the thermal interval 1200-800 °C, followed by rapid cooling. Thermal runs were performed in reducing atmosphere (fO₂ 10−8-10−15 bars) created by a continuous flow of a CO2:H2 mix with a ratio of 100:4 (cm3/min). Ten experiments were successfully carried out and hundreds of inclusion-free gem-quality single crystals (up to 1 mm large) were produced in each of them, sometimes together with crusty aggregates and microcrystalline powder. Selected crystals were investigated by SEM/EDS X-ray mapping to check for compositional homogeneity and by electron-microprobe analysis to obtain the chemical formula. Crystals were found to be chemically homogeneous and entirely representing the MgAl2O4-CoAl2O4 solid-solution series, with the latter component ranging from 7 to 100%. With increasing Co2+ contents, the crystals vary in color from light blue to intensely dark blue in daylight. The unit-cell parameter a increases from 8.084 to 8.105 Å along the solid-solution series, and the observed increase is determined more by the inversion degree than by the variation in Co contents. The composition of crystal products does not correspond to the composition of the starting oxide mixture, being cobalt enriched in the crystals. A tentative explanation of this behavior is suggested by considering possible ionic potential as well crystal field stabilization effects.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Cation ordering over short-range and long-range scales in the MgAl2O4-CuAl2O4 series
- Blue spinel crystals in the MgAl2O4-CoAl2O4 series: Part I. Flux growth and chemical characterization
- Blue spinel crystals in the MgAl2O4-CoAl2O4 series: Part II. Cation ordering over short-range and long-range scales
- CO2 solubility in primitive martian basalts similar to Yamato 980459, the effect of composition on CO2 solubility of basalts, and the evolution of the martian atmosphere
- New structural features of the high-pressure synthetic sheet-disilicate Phase-X, K(2–x)Mg2Si2O7Hx
- Crystal structure refinements of borate dimorphs inderite and kurnakovite using 11B and 25Mg nuclear magnetic resonance and DFT calculations
- Hydrogen-bond system and dehydration behavior of the natural zeolite parthéite
- In situ dehydration behavior of zeolite-like cavansite: A single-crystal X-ray study
- LREE-redistribution among fluorapatite, monazite, and allanite at high pressures and temperatures
- A single-crystal neutron diffraction study of hambergite, Be2BO3(OH,F)
- Analyzing water contents in unexposed glass inclusions in quartz crystals
- The atomic structure of deuterated boyleite ZnSO4·4D2O, ilesite MnSO4·4D2O, and bianchite ZnSO4·6D2O
- Synthesis and crystal chemistry of Fe3+-bearing (Mg,Fe3+)(Si,Fe3+)O3 perovskite
- Mixed-layered structure formation during trans-vacant Al-rich illite partial dehydroxylation
- Structural regularities in 2M1 dioctahedral micas: The structure modeling approach
- Incorporation of Fe and Al in MgSiO3 perovskite: An investigation by 27Al and 29Si NMR spectroscopy
- In situ high-temperature Raman and FTIR spectroscopy of the phase transformation of lizardite
- Packing systematics and structural relationships of the new copper molybdate markascherite and related minerals
- On the origin of sellaite (MgF2)-rich deposits in Mg-poor environments
- Edgrewite Ca9(SiO4)4F2-hydroxyledgrewite Ca9(SiO4)4(OH)2, a new series of calcium humite-group minerals from altered xenoliths in the ignimbrite of Upper Chegem caldera, Northern Caucasus, Kabardino-Balkaria, Russia
- Whelanite, Cu2Ca6[Si6O17(OH)](CO3)(OH)3(H2O)2, an (old) new mineral from the Bawana mine, Milford, Utah
- 2M1-phlogopite from Black Hills (South Australia): The first case of configurational polytype in micas
- Oxy-chromium-dravite, NaCr3(Cr4Mg2)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup
- First-principles study of self-diffusion and viscous flow in diopside (CaMgSi2O6) liquid
- Browneite, MnS, a new sphalerite-group mineral from the Zakłodzie meteorite
- Mineralogical variation of silica induced by Al and Na in hydrothermal solutions
Articles in the same Issue
- Cation ordering over short-range and long-range scales in the MgAl2O4-CuAl2O4 series
- Blue spinel crystals in the MgAl2O4-CoAl2O4 series: Part I. Flux growth and chemical characterization
- Blue spinel crystals in the MgAl2O4-CoAl2O4 series: Part II. Cation ordering over short-range and long-range scales
- CO2 solubility in primitive martian basalts similar to Yamato 980459, the effect of composition on CO2 solubility of basalts, and the evolution of the martian atmosphere
- New structural features of the high-pressure synthetic sheet-disilicate Phase-X, K(2–x)Mg2Si2O7Hx
- Crystal structure refinements of borate dimorphs inderite and kurnakovite using 11B and 25Mg nuclear magnetic resonance and DFT calculations
- Hydrogen-bond system and dehydration behavior of the natural zeolite parthéite
- In situ dehydration behavior of zeolite-like cavansite: A single-crystal X-ray study
- LREE-redistribution among fluorapatite, monazite, and allanite at high pressures and temperatures
- A single-crystal neutron diffraction study of hambergite, Be2BO3(OH,F)
- Analyzing water contents in unexposed glass inclusions in quartz crystals
- The atomic structure of deuterated boyleite ZnSO4·4D2O, ilesite MnSO4·4D2O, and bianchite ZnSO4·6D2O
- Synthesis and crystal chemistry of Fe3+-bearing (Mg,Fe3+)(Si,Fe3+)O3 perovskite
- Mixed-layered structure formation during trans-vacant Al-rich illite partial dehydroxylation
- Structural regularities in 2M1 dioctahedral micas: The structure modeling approach
- Incorporation of Fe and Al in MgSiO3 perovskite: An investigation by 27Al and 29Si NMR spectroscopy
- In situ high-temperature Raman and FTIR spectroscopy of the phase transformation of lizardite
- Packing systematics and structural relationships of the new copper molybdate markascherite and related minerals
- On the origin of sellaite (MgF2)-rich deposits in Mg-poor environments
- Edgrewite Ca9(SiO4)4F2-hydroxyledgrewite Ca9(SiO4)4(OH)2, a new series of calcium humite-group minerals from altered xenoliths in the ignimbrite of Upper Chegem caldera, Northern Caucasus, Kabardino-Balkaria, Russia
- Whelanite, Cu2Ca6[Si6O17(OH)](CO3)(OH)3(H2O)2, an (old) new mineral from the Bawana mine, Milford, Utah
- 2M1-phlogopite from Black Hills (South Australia): The first case of configurational polytype in micas
- Oxy-chromium-dravite, NaCr3(Cr4Mg2)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup
- First-principles study of self-diffusion and viscous flow in diopside (CaMgSi2O6) liquid
- Browneite, MnS, a new sphalerite-group mineral from the Zakłodzie meteorite
- Mineralogical variation of silica induced by Al and Na in hydrothermal solutions
