A Study of Weathering in a Soil Derived from a Biotite-Hornblende Rock

Abstract

The weathering of hornblende in the Rehiran profile has been investigated by optical, X-ray, infrared and differential thermal methods. Optical studies of the fresh hornblende show that it contains discrete lamellar intergrowths of another amphibole which, from infrared evidence, is of an iron-rich nature. This minor phase is selectively weathered in the lower horizons and yields a clay mineral which was identified as interstratified swelling chlorite-saponite. The major hornblende component remains relatively unchanged. Single crystal photographs indicate that the formation of the clay mineral is not structurally controlled by the parent hornblende, although there is a tendency towards alignment along cleavage planes. The clay mineral becomes unstable in the upper part of the profile and could not be detected in the A horizon. Comparisons are made with the findings of other workers.

Rates and nonstoichiometry of vermiculite dissolution at 22°C

“…As indicated by numerous studies (e.g. Wilson, 1970;Churchman, 1980) regularly interstratified hydromicas have increased weathering resistance compared to pure K-micas. Their stability has been attributed to an increased fixation of K in interlayers adjacent to K-depleted interlayers due to reorientation of OH protons in the octahedral sheet in direction of the hydrated interlayer (Norrish, 1973).…”

Interstratified vermiculite–mica in the gneiss–metapelite–serpentinite rocks at Hafafit area, Southern Eastern Desert, Egypt: From metasomatism to weathering

“…Sequence of mineral zones and the mutual relations between chlorite/vermiculite (corrensite) and other phases conclude that the mixed-layer chlorite/vermiculite might be formed from biotite or phlogopite (Wilson, 1970). However, occurrence of most chlorite-vermiculite interstratifications closer to the serpentinite and metapelite rocks concludes that mixed-layer chlorite/vermiculite most probably formed by alteration of chlorite (Weaver, 1989).…”

Electron microscope and microprobe analysis of chlorite–mica stacks in the Wenlock turbidites, mid Wales, U.K.

“…Biotite alteration to vermiculite and then chlorite is an accepted alteration sequence during both weathering (Wilson, 1970) and diagenesis (Kisch, 1983). Wilson (1970) showed that during the early stages of weathering in soil environments, biotite expands to a 14 A phase (hydrobiotite).…”