Reference Chlorite Characterization for Chlorite Identification in Soil Clays

Abstract

Literature pertaining to differential thermal and X-ray diffraction of chlorite minerals is reviewed. Optical, DTA, and X-ray data for eleven chlorite samples of clinochlore, prochlorite, thuringite, corundophilite, and leuchtenbergite are given. The effect of particle size (105 to-1 ~) on DTA, X-ray diffraction, glycol retention, and cation exchange capacity are given for two thuringites, one clinochlore, and one prochlorite. Identification of chlorite by DTA in a soil clay containing a mixture of minerals is improbable at the present time except under very favorable circumstances. However, for relatively pure chlorite samples, variations in chemical composition are reflected in the differential thermal curves. The largest change in the thermogram is produced by ferric iron which lowers the peak temperature from 720 ~ C to 610 ~ C. Differences in thermal behavior between low and high ferric iron chlorite species are maintained for any given particle size; Chlorite thermograms obtained by different investigators show much greater variation than the differences in thermograms for other clay minerals determined on different equipment. X-ray diffraction can be used to positively identify chlorite in a soil clay, (a) by careful analysis of reflections at least as great as 14 A, and (b) by the influence heat treatment (550 ~ C for 30 minutes) has on the X-ray pattern. Heat treatment produces marked changes in the X-ray pattern of the finer particle size samples and the magnitude of the change effected is greater for high iron chlorites (thuringite) than for low iron chlorites (clinochlore and prochlorite). Olivine is not the recrystallization product for thuringite. The smallest size fractions show no tendency toward vermiculite or montmorillonoid. Cation exchange capacity for silt size chlorites varies from 4 to 32 m.e./100gm., and for-2 ~ chlorite particles from 30 to 47 m.e./100gm. Cation exchange capacities for-2 ~ and-1 ~ chlorites are essentially the same. Ethylene glycol retention increases with decreasing particle size. Glycol retention for-2 ~ chlorite samples varies from 25 to 40 mg. glycol/gm, clay. For-1 /z chlorite material, glycol retention is 2 to 4 times greater than for-2 # material.

The Chlorite Series of Flagstaff Hill Area, California: A Preliminary Investigation

“…All temperatures given are those of the peak temperatures and not the commencement of the peak. The exothermic reaction peaks observed for the chlorite samples from Flagstaff Hill area appear to be significantly higher than those given by Mackenzie (1966) and Grim (1968), but only slightly higher than those given by Martin (1955). This discrepancy may be due to the heating rate used (20~ per min) being higher than the more customary rate of 10~176 per min.…”

Mineralogical Analysis of Soil Clays Involving Vermiculite-Chlorite-Kaolinite Differentiation

“…Martin (1955, p. 138) reported glycol sorption values ranging from 6 to 106 mg per g and cation exchange values from 3.8 to 47 meq per 100 g for various size fractions of chlorites. The instances reported of some collapse of chlorites on heating together with the rather high cation exchange and glycerol sorption values reported by Martin (1955) indicate the presence of collapsible layers interstratified with chlorite layers even in samples selected for properties typical of chlorite. Bradley (1954, p. 328) reports collapse of some layers of a chlorite from a sediment owing to incomplete filling of the brucite layer.…”

“…Some collapse of typical chlorite on heating has been reported (Martin, 1955;Brindley and Robinson, 1951, p. 195); collapse of sedimentary chlorite also has been reported (Bradley, 1954, p. 328). Martin (2955, pp.…”

Characterization of pulverized granitoids in a shallow core along the San Andreas Fault, Littlerock, CA

“…All of the diffractograms for core samples, regardless of depth or type, contain chlorite (14.25, 7 and 4.8 Å). It is possible that the peak at 7 Å represents kaolinite as well, being that both kaolinite and Fe‐rich chlorite collapse when heated to 550° (Martin 1955). All of the granite samples contain illite (characteristic peaks at 10.1 and 5 Å), although it could possibly be a mica, for instance muscovite, which was observed in thin sections.…”