Banded minerals

Onyx Another microcrystalline banded mineral, having... 

Gr. prasios, green, and didymos, twin) In 1841 Mosander extracted the rare earth didymia from lanthana in 1879, Lecoq de Boisbaudran isolated a new earth, samaria, from didymia obtained from the mineral samarskite. Six years later, in 1885, von Welsbach separated didymia into two others, praseodymia and neodymia, which gave salts of different colors. As with other rare earths, compounds of these elements in solution have distinctive sharp spectral absorption bands or lines, some of which are only a few Angstroms wide. 

L. Holmia, for Stockholm). The special absorption bands of holmium were noticed in 1878 by the Swiss chemists Delafontaine and Soret, who announced the existence of an "Element X." Cleve, of Sweden, later independently discovered the element while working on erbia earth. The element is named after cleve s native city. Holmia, the yellow oxide, was prepared by Homberg in 1911. Holmium occurs in gadolinite, monazite, and in other rare-earth minerals. It is commercially obtained from monazite, occurring in that mineral to the extent of about 0.05%. It has been isolated by the reduction of its anhydrous chloride or fluoride with calcium metal. 

Infrared spectroscopy can also be used incisively to identify the six main varieties of asbestos fibers. Specific absorption bands in the infrared spectmm can be associated with the asbestos fibers, first in the 3600 3700 cm range (specific hydroxyl bands) and, second, in the ranges 600—800 and 900 1200 cm (specific absorption bands for various siUcate minerals (10)). 

Substance CAS Registry Number Mineral name Pigment name Band gap, eV Color... 

A pure transition metal is best described by the band theory of solids, as introduced in Chapter 10. In this model, the valence s and d electrons form extended bands of orbitals that are delocalized over the entire network of metal atoms. These valence electrons are easily removed, so most elements In the d block react readily to form compounds oxides such as Fc2 O3, sulfides such as ZnS, and mineral salts such as zircon, ZrSi O4. ... 

Mercuric sulfide (HgS) is dimorphic. The more common form, cinnabar (red a-form), has a distorted RS, trigonal structure which is unique among the monosulfides, for the crystal is built of helical chains in which Hg has two nearest neighbors at 2.36 A, two more at 3.10 A, and two at 3.30 A. Bulk a-HgS is a large-gap semiconductor (2.1 eV), transparent in the red and near IR bands. The rare, black mineral metacinnabarite is the 3-HgS polymorph with a ZB structure, in which Hg forms tetrahedral bonds. Upon heating, 3-HgS is converted to the stable a-form. The ZB structure of HgS is stabilized under a few percent admixture of transition metals, which replace Hg ions in the lattice. 

Lead(II) sulfide occurs widely as the black opaque mineral galena, which is the principal ore of lead. The bulk material has a band gap of 0.41 eV, and it is used as a Pb " ion-selective sensor and IR detector. PbS may become suitable for optoelectronic applications upon tailoring its band gap by alloying with II-VI compounds like ZnS or CdS. Importantly, PbS allows strong size-quantization effects due to a high dielectric constant and small effective mass of electrons and holes. It is considered that its band gap energy should be easily modulated from the bulk value to a few electron volts, solely by changing the material s dimensionality. 

Principal gangue minerals in base-metal vein-type deposits are quartz, chlorite, Mn-carbonates, calcite, siderite and sericite (Shikazono, 1985b). Barite is sometimes found. K-feldspar, Mn-silicates, interstratified mixed layer clay minerals (chlorite/smectite, sericite/smectite) are absent. Vuggy, comb, cockade, banding and brecciated textures are commonly observed in these veins. 

The vein is composed of rhythmic banding of quartz layers and fine-grained sulfides such as argentite, acanthite, sphalerite, galena, pyrite and chalcopyrite, and elec-trum. The principal gangue minerals are quartz, calcite, adularia and interstratified chlorite/smectite. Minor minerals are inesite, johansenite, xonotlite and sericite. These gangue minerals except for quartz, adularia, calcite and sericite are not found in the wall rocks. 

The veins are composed mostly of quartz and a small amount of sulfide minerals (pyrite, pyrrhotite, arsenopyrite, chalcopyrite, sphalerite, and galena), carbonate minerals (calcite, dolomite) and gold, and include breccias of the host rocks with carbonaceous matters. Layering by carbonaceous matters has been occasionally observed in the veins. Banding structure, wall rock alteration and an evidence of boiling of fluids that are commonly observed in epithermal veins have not been usually found. 

Main opaque minerals are chalcopyrite, pyrite, pyrrhotite, sphalerite and bornite (Table 2.22). These minerals commonly occur in massive, banded and disseminated ores and are usually metamorphosed. Hematite occurs in red chert which is composed of fine grained hematite and aluminosilicates (chlorite, stilpnomelane, amphibole, quartz) and carbonates. The massive sulfide ore bodies are overlain by a thin layer of red ferruginous rock in the Okuki (Watanabe et al., 1970). Minor opaque minerals are cobalt minerals (cobaltite, cobalt pentlandite, cobalt mackinawite, carrollite), tetrahedrite-tennantite, native gold, native silver, chalcocite, acanthite, hessite, silver-rich electrum, cubanite, valleriite , and mawsonite or stannoidite (Table 2.22). 

In general electrum is rare, but it is found in some deposits such as the Shimokawa, Besshi, and Yanahara (Urashima, 1974). A detailed study on the mode of occurrence of electrum has been carried out only on the Shimokawa deposit (Maeda et al., 1981). Flectrum occurs in compact massive or banded ores in the upper horizon. This mineral is intimately associated with sphalerite and pyrrhotite. Analytical data on electrum are available only from the Shimokawa (Maeda et al., 1981). The Ag content ranges from 22.2 to 71.6 atomic %, but average content is ca. 30 atomic %. This variation range is... 

Dihydroepistephamiersine 6-acetate (7) was isolated from Stephania abyssinica as a homogeneous oil. The UV spectrum showed an absorption maximum at 286 nm, and the IR spectrum exhibited a band corresponding to an aliphatic ester carbonyl group at 1725 cm-1 (20). The H-NMR data are summarized in Table II. In chemical investigations, hydrolysis of 7 with barium methoxide gave an alcohol identical with 6-dihydroepistephamiersine (17), which on further treatment with mineral acid gave the known alkaloid, stephasunoline (17). Thus structure 7 was proposed for 6-dihydroepistephamiersine 6-acetate (20). 

Mineral Colour Most intense X-ray lines IR bands (cm 1) Magnetic hyperfine field (T) ... 

In the X-ray powder diffraction patterns of the composites, the disappearance of the broad band centered at 22 °20, typical of amorphous silica, indicates that the zeolitisation of the mineral fraction of the parent composite was complete. In no diffraction pattern any sign of crystallised chitosan could be found. The two methods in which the silica-polymer beads were extracted from the aluminate solution after impregnation (methods A and C) allowed the formation of the expected zeolite X, with traces of gismondine in the case of the method C. The method B, in which excess aluminate solution was present during the hydrothermal treatment, resulted in the formation of zeolite A. 

The mineral oil absorption at 2800 to 3000 cm- 1 and at 1460 cm- obscures absorption bands of hydralazine hydrochloride at 2810, 2920, and 2970 cm-1 (N-H+ stretch) and a weak sharp band at 1470 cm- these bands can be observed in potassium bromide dispersion spectra. The bands at 1070 and 1082 cm-1 tend to merge into a single band in potassium bromide dispersion spectra. 

The infrared spectrum of hydralazine hydrochloride base in a potassium bromide dispersion (Figure 2) was recorded from 400 to 4000 cm-1, and the 200 to 550 cm-1 region was obtained from a mineral oil dispersion supported on polyethylene film. The spectra of potassium bromide dispersions of the base are qualitatively identical to those of mineral oil dispersions. The assignment of absorption bands in the spectrum of the base is similar+to that of the hydrochloride except for the presence of N-H stretch absorption in the latter. A spectrum of the base has been published (6). 

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