Changbaiite
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| Changbaiite | |
|---|---|
 | |
| General | |
| Category | Oxide minerals |
| Formula | PbNb2O6 |
| Strunz classification | 4.DF.10 |
| Crystal system | Trigonal |
| Crystal class | Ditrigonal pyramidal (3m) (same H-M symbol) |
| Space group | R3m |
| Identification | |
| Formula mass | 489.01 gram/mol |
| Color | Colorless, Cream white, Pale brown, Yellow brown, Pale yellow green |
| Crystal habit | Tabular - Form dimensions are thin in one direction. |
| Cleavage | {0001} Perfect, {1011} Distinct |
| Mohs scale hardness | 5.5 |
| Luster | Adamantine - Pearly |
| Streak | white |
| Diaphaneity | Transparent |
| Optical properties | Uniaxial (+), w=2.476, e=2.485, bire=0.0090. |
| Ultraviolet fluorescence | Non-fluorescent |
| References | [1][2][3][4] |
Changbaiite (PbNb2O6) is a member of the oxide mineral class in which the mineral contains oxygen which is grouped along with one or two metal ion. Changbaiite is classified as a multiple Oxide XY2O6 and it generally has an ionic bond.[5] Furthermore, it is also orthorhombic at a temperature of 25 °C and it changes to orthorhombic-tetragonal at 570 °C.[6]
The chemical formula of changbaiite is PbNb2O6 after microprobe analysis of kaolinite-filled veins. It is composed of iron (II) oxide FeO 0.94%, lead oxide PbO 41.51%, iron (III) oxide Fe2O3 0.42%, titanium dioxide TiO2 0.95%, niobium pentoxide Nb2O5 55.62%, and tantalum pentoxide Ta2O5 0.98%, which produce the chemical formula (Pb0.95Fe2+0.05)(Nb1.95Ti0.05Fe3+0.02Ta0.01) or PbNb2O6. It was also examined by the spectrographic method which represents Sb 0.3, Si 0.1, Ba 0.2, Ca 0.1, and minor traces of copper, magnesium and aluminum.[7]
Subbarao suggested that Changbaiite formula PbNb2O6 can vary. He represented lead niobate by A1+xNb2O6 where the A site is an ion (usually lead) and he found that the upper limit of x in his representation was about 0.15 and a low limit between −0.07 and −0.08. In conclusion, the formula ranges from Pb0.92Nb2O6 to Pb1.15Nb2O6.[6]
Geological occurrence
Atomic structure
According to Subbarao,[6] changbaiite is orthorhombic at 25 °C with unit cell dimensions of a=17.65, b=17.91, c=7.736 Å and because its big unit cell size it is difficult to do a full structure analysis of PbNb2O6.[6] Changbaiite structure is composed of NbO6 octahedral crystals connected at their corners forming circles of 3 to 5 octahedral.[6] The NbO6 "cage" has coordination of 8 around oxygen. and the "tunnels" have a coordination of 10 around the Pb2+.[6]