Chlorites composition

Chlorite compositions from areas (Toyoha Pb—Zn vein, Kuroko deposits) deviate significantly from a line of 1 1 slope. This deviation implies that the Fe +/Mg value of chlorite from these areas is controlled not only by the FeO/MgO value of the Ifesh host rocks, but also by factors such as the ratio of Fe " to Mg " " in the fluid phase. 

Fig. 2.51. Plot of chlorite compositions on the diagram proposed by Hey (1954). The compositional range of chlorite in the metasomatized ba.salt from midocean ridges is taken from Humphris and Thompson (1978) (Shinozuka et al., 1999).

Figure 30. Comparison range of 7-14 8 chlorite compositions in the Mg-Si-A1 system (Velde, 1973). Dots show composition of berthierine pellets in these coordinates.

Figure 31b. Compositions of chlorites in the mixed-layered mineral facies of pelitic rocks (circles) and from the illite-chlorite facies (barred circles). Shaded area shows chlorite compositions from muscovite-chlorite metamorphic rocks.

It is possible that the mechanism of berthierine formation in this example is one of accretion, i.e., the grain would accumulate material at the exterior and this is eventually transformed into a chlorite composition. None of the grains was noted to have the form of a shell test as is often noted glauconite pellets. However the meta-berthierine pellets reported by Velde, et al.. (1974), were often found inside foraminifera tests. 

This has been confirmed in the present study for chlorites from six rocks from the Belt series in northern Montana (Harrison and Jobin, 1963) and three samples from the outer zones in the Alpine chain. From these analyses, it is apparent that metamorphic chlorites which have crystallized with muscovite have low silica contents and a rather limited alumina content (27 3% A1 ions). The relatively large variation in chlorite Fe-Mg ratio from rock to rock suggests that bulk rock composition is more important in determining the chlorite composition than is the case of chlorites from clay mineral facies. 

Although the information available from synthetic studies strongly indicates a P-T control of the chlorite polymorph, natural minerals appear to exhibit both polymorph, 7 and 14 8, at low temperature. Most diagenetic chlorites correspond to a 7 8 polymorph. However, there are occurrences especially in deep ocean sediments of a 14 8 phase. The contradiction cannot be resolved with the information available at present. It is probably reasonable to assume that the 7 8 polymorph stable for all chlorite compositions (i.e., various Fe +, Mg, A1 ratios) and that the 14 8 forms are metastable at low temperatures. However, this is certainly not definitive. 

In the central part of the Illizi Basin and over the Ghadames Depression (WT-i, HD-i, RYB-i, AKF-i) we observe sediments characteristic of deeper marine environments, i.e. fine-grained sandstones with intercalations of clays and silts. The characteristic feature of these Siegenian sandstones is the chloritic composition of the clay fraction of their cements and the chloritic-illitic nature of the argillaceous intercalations. Because of this situation, these deposits could have been derived from a hard substrate (effusive or metamorphic rocks) inundated by the Siegenian sea and open into the direction of the present Libyan coast. 

Figure 6.14 Patterns observed in the chlorite-iodide-malonic acid reaction in a Couette reactor. The CSTR composition, flow rate, and rotation rate are held fixed, except for chlorite composition in one CSTR, whieh serves as the bifurcation parameter. In each frame, the abscissa represents the position along the reactor and the ordinate represents time. The dark color results from the presence of the starch- triiodide complex. (Adapted from Ouyang et al., 1991.)...

The latter assumption is not valid in terms of our modern knowledge of chlorite compositions. 

Figure 5. Chlorite compositions according to structural unit type (Bailey and Brown [1962]). Compositions determined by X-ray spacing graphs, (a) lift structural type (b) all other structural types relative to the IK compositional field determined in (a).

Disinfectant Formulations and Sterilization. Hundreds of appHcations covering disinfectant compositions using sodium chlorite have been described in U.S. and foreign patents. Some examples of these are as antimicrobial additives for latexes (166), marine antifouling agents (see Coatings, marine) (167,168), antimildew detergent compositions (169), toothpaste and solution compositions for prevention and treatment of periodontal oral disease (see Dentifrices) (170—172), and compositions for the disinfection of contact lenses (qv) (173). 

Chlorine dioxide gas generated from chlorite has been used as a chemosterilizing agent substitute for ethylene oxide in medical appHcations (174,175). Aqueous foam compositions containing chlorine dioxide have also been developed for the sanitization of hard surfaces (176). 

Vermicuhte is an expandable 2 1 mineral like smectite, but vermiculite has a negative charge imbalance of 0.6—0.9 per 02q(0H)2 compared to smectite which has ca 0.3—0.6 per 02q(0H)2. The charge imbalance of vermiculite is satisfied by incorporating cations in two water layers as part of its crystal stmcture (144). Vermiculite, which can be either trioctahedral or dioctahedral, often forms from alteration of mica and can be viewed as an intermediate between UHte and smectite. Also, vermiculite is an end member in a compositional sequence involving chlorite (37). Vermiculite may be viewed as a mica that has lost part of its K+, or a chlorite that has lost its interlayer, and must balance its charge with hydrated cations. 

Chlorite is another mineral that is commonly associated with mixed-layered clays. Complete soHd solutions of chlorite mixed-layer minerals have not been identified. In contrast to iUite—smectite mixed-layer minerals, chlorite mixed-layer minerals occur either as nearly equal proportions of end-member minerals (Rl) or dominated by one end member (RO) (142). Mixed-layer chlorite may consist of any of the di—tri combinations of chlorite and chlorite mixed-layering occurs with serpentine, kaolinite, talc, vermicuhte, smectite, and mica. References of specific chlorite mixed-layer minerals of varied chemical compositions are available (142,156). 

Figure 1.29. Calculated changes in the S 0 values of volcanic rocks (5 0 = +7.0%c) as a result of equilibrium oxygen isotope exchange with waters of different initial compositions. The dotted areas represent the ranges of rocks in the zeolite and the sericite-chlorite zones (Green et al., 1983).

Several factors such as Cl concentration, water/rock ratio and temperature are important in controlling the chemical composition of the hydrothermal solution interacted with the rocks. For example, water/rock ratio affects the alteration mineralogy (Mottl and Holland, 1978 Seyfried and Mottl, 1982 Shikazono, 1984). For example, at low water/rock ratio, epidote is stable, while chlorite at high water/rock ratio (Shikazono, 1984 Shikazono and Kawahata, 1987). 

Consequently, the composition of chlorite in the discharge zone depends largely on the chemical nature of fluids (factors such as Fe "/Mg, SO /H2S, pH, aj 2+) and temperature. Movement of fluids may also be an important cause for the variability in the ratio of Fe " to Mg in hydrothermal chlorite. Wide compositional variations in chlorite from the hydrothermal ore deposits in Japan, including Kuroko and Neogene Cu-Pb-Zn vein-type deposits, are considered to reflect the variable chemical nature of ascending ore fluids and fluids that mix with ascending ore fluids at discharge zone. 

The variations in Fe and Mg contents of the 14 A Fe-chlorite-14 A Mg-chlorite solid solution are considered here. However, structural formulae for chlorite are not as simple as those considered here. As mentioned by Walshe and Solomon (1981), Stoesell (1984), Cathelineau and Nieva (1985) and Walshe (1986), chlorite solid solution may be represented by six components, and accurate thermochemical data on each end-member component at the hydrothermal conditions of concern are necessary to provide a far more rigorous calculation of the equilibrium between chlorite and hydrothermal solution. However, the above argument demonstrates that the composition of chlorite is a highly useful indicator of physicochemical conditions of hydrothermal solution and extent of water-rock interaction. 

Figure 1.170. Diagram showing the octahedral composition of chlorites from the subvolcanrc hydrothermal deposits, propylite, and Kuroko deposits in Japan (Nakamura, 1970). Chlorite occurring as a gangue mineral in the subvolcanic hydrothermal deposits Nos. 1, 2, 3 and 4 Chlorite from the Ashio copper mine. Nos. 5, 6, and 7 Chlorite from the Kishu mine. No. 8 Chlorite from the Arakawa mine. Nos. 9 and 10 Chlorite from the Ani mine. No. 11 Chlorite from the Osarizawa mine. Chlorite from the so-called propylite No. 12 Chlorite from the Yugashima mine. No. 13 Chlorite from the Budo mine. Chlorite from the Kuroko deposits No. 14 Chlorite from the Wanibuchi mine.

Hayashi, H. and Oinuma, K. (1965) Relationship between infrared absorption spectra in the region of 450-900 cm and chemical composition of chlorite. Am. Mineral, 50, 476-483. 

Hayashi, M. (1979) Chemical composition of chlorite in altered rocks in Chitose and Ohe deposits. Earth Sci. (Japan), 33, 102-103 (in Japanese). 

Shikazono, N. and Kawahata, H. (1987) Compositional differences in chlorite from hydrotheimally altered rocks and hydrothermal ore deposits. Can. Mineral. 25, 465-474. 

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