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A study demonstrates that by carefully optimizing the reaction condition, it is possible to selectively fabricate niobate structures of high purity, including the delicate microporous fibers, through a direct reaction between concentrated NaOH solution and Nb2O6 units. Nioblates with different structures are found to exhibit remarkable differences in light absorption and photoluminescence properties.

Raman and infrared active modes of cerussite were assigned according to their symmetry species and compared to other aragonite group minerals. Small satellite bands at 823 and 1031 [cm.sup.-1] on the low-wavenumber side of the fundamental vibrations [V.sub.2] and [V.sub.1], respectively, have been assigned to the isotopic substitutions of [sup.13]C and [sup.18]O. The Raman active [V.sub.1] and [V.sub.2] carbonate modes are observed at 1051 and 835 [cm.sup.-1]. The absence of the [B.sub.2g] component of the [V.sub.1] and [V.sub.2] vibrations has been explained by the small coupling between the [A.sub.g] and [B.sub.2g], modes. The Raman active [V.sub.3] carbonate anti-symmetric stretching mode is observed at 1361([A.sub.g]), 1376 ([B.sub.1g]), 1419 ([B.sub.3g]), and 1477 ([B.sub.2g]) [cm.sup.-1], while the corresponding infrared active bands are observed at 1396, 1432, and 1456 [cm.sup.-1]. The Raman active [V.sub.4] carbonate bending mode is observed at 673 ([A.sub.g]), 668 ([B.sub.2g]), 681 ([B.sub.1g]), and 694 ([B.sub.2g] [cm.sup.-1]. The corresponding infrared bands are observed at 670, 679, and 698 [cm.sup.-1]. In both [V.sub.3] and [V.sub.4] the factor group splitting between the [B.sub.1g] and [B.sub.3g] modes is 1 to 3 times smaller than the separation of the [A.sub.g] and [B.sub.2g] modes. Raman active lattice vibrations are detected at 120 ([B.sub.3g]), 132 ([A.sub.g]), 148 ([B.sub.1g]), 152([B.sub.2g]), 174 ([B.sub.2g]), 179 ([B.sub.1g]), 213 ([A.sub.g]), 226 ([B.sub.3g]), and 243 [cm.sup.-1] ([B.sub.2g]). Corresponding infrared active bands are detected at 573, 543, 573, 423, 375, 290, 205, 165, 146, and 134 [cm.sup.-1]. Raman bands at 949, 966, 989, 1000, and 1104 [cm.sup.-1] and at 922, 946, 967, 988, 996, and 1007 [cm.sup.-1] in the infrared spectra are assigned to combination and overtone bands. Raman bands at 1676 ([A.sub.g]), 1689 ([A.sub.g]), 1730 ([B.sub.3g]), and 1740 ([B.sub.1g]) [cm.sup.-1] are ascribed to combination modes of [V.sub.1] + [V.sub.4] with bands at 2052 and 2092 [cm.sup.-1] assigned to 2[V.sub.1]. Corresponding infrared bands are observed at 1729 and 1740 [cm.sup.-1] ([V.sub.1] + [V.sub.3]). Bands at 2359, 2409, 2471, and 2521 [cm.sup.-1] are ascribed to [V.sub.1] + [V.sub.3], with broad bands at 1246 and 1323 [cm.sup.-1] assigned to 2[V.sub.4] modes.

Gorgeyite, [K.sub.2][Ca.sub.5][(S[O.sub.4]).sub.6]*[H.sub.2]O, is a very rare monoclinic double salt found in evaporites related to the more common mineral syngenite. At 1 atmosphere with increasing external temperature from 25 to 150[degrees]C, the following succession of minerals was formed: first gypsum and [K.sub.2]O, followed at 100[degrees]C by gorgeyite. Changes in concentration at 150[degrees]C due to evaporation resulted in the formation of syngenite and finally arcanite. Under hydrothermal conditions, the succession is syngenite at 50[degrees]C, followed by gorgyeite at 100 and 150[degrees]C. Increasing the synthesis time at 100[degrees]C and 1 atmosphere showed that initially gypsum was formed, later being replaced by gorgeyite. Finally gorgeyite was replaced by syngenite, indicating that gorgeyite is a metastable phase under these conditions. Under hydrothermal conditions, syngenite plus a small amount of gypsum was formed, after two days being replaced by gorgeyite. No further changes were observed with increasing time. Pure gorgeyite showed elongated crystals approximately 500 to 1000 [micro]m in length. The infrared and Raman spectra are mainly showing the vibrational modes of the sulfate groups and the crystal water (structural water). Water is characterized by OH-stretching modes at 3526 and 3577 [cm.sup.-1], OH-bending modes at 1615 and 1647 [cm.sup.-1], and an OH-libration mode at 876 [cm.sup.-1]. The sulfate [v.sub.1] mode is weak in the infrared but showed strong bands at 1005 and 1013 [cm.sup.-1] in the Raman spectrum. The [v.sub.2] mode also showed strong bands in the Raman spectrum at 433, 440, 457, and 480 [cm.sup.-1]. The [v.sub.3] mode is characterized by a complex set of bands in both infrared and Raman spectra around 1150 [cm.sup.-1], whereas [v.sub.4] is found at 650 [cm.sup.-1].

Molecular structures of the basic copper arsenate minerals olivenite, cornubite, cornwallite, and clinoclase were studied using a combination of infrared emission spectroscopy and Raman spectroscopy. Infrared emission spectra of the basic copper arsenates were obtained over the temperature range 100 to 1000[degrees]C. The IR emission spectra of the four minerals are different, in line with differences in crystal structure and composition. The Raman spectra are similar, particularly in the OH-stretching region, but characteristic differences in the deformation regions are observed. Differences are also observed in the arsenate stretching and bending regions. Infrared emission studies show that the minerals are completely dehydroxylated by 550[degrees]C.