Weathering of Basalt: Formation of Iddingsite

Abstract

Abstract--The formation of iddingsite by the oxidative weathering of FoB0 olivine begins by solution of Mg from planar fissures, 20 ~ wide and spaced 200 ~ apart, parallel to (001). Oxidation of Fe within the remaining olivine provides nuclei for the topotactic growth of goethite. Cleavage cracks <50 ~ in diameter allow Na, AI, and Ca from adjacent minerals, particularly plagioclase, to enter the altering olivine while Mg and Si diffuse away. In the early stages of weathering, strips of Fe-rich smectite (saponite), 20-50 & wide and 1-7 layers thick, form bridges 50-100 ~. long across the planar fissures. Dioctahedral smectite crystallizes on the margins of wider cleavage-controlled fissures; with further weathering halloysite is formed away from the fissure walls. In the ultimate stages of alteration, the saponite and dioctahedral smectite are lost, leaving a porous, oriented aggregate of goethite crystals each measuring about 50 • 100 • 200 A (X, Y, Z, respectively), with sporadic veins of halloysite crossing the pseudomorph.

Influence of Anionic Layer Structure of Fe-Oxyhydroxides on the Structure of Cd Surface Complexes

“…However, {010} faces are infrequent and minute (especially for the Cornwall specimen goethite (16)), implying that they are relatively unstable. This is consistent with the observation that goethite crystallites are often diamond-shaped in cross-section, looking down the needle c axis (19)(20)(21)(22) (Fig. 1a).…”

“…The crystal faces were indexed in the early 20th century shortly after the invention of X-ray techniques (14,15), and the original choice of crystallographic axes has been retained (7,8,(16)(17)(18). Natural and synthetic goethite crystals are bounded primarily by {110} faces and secondarily by {100} faces, which (19,21,22) and synthetic (20) goethite crystals. (2) Synthetic form obtained by Weidler et al (7,8).…”

“…run parallel to the length of the crystals (19)(20)(21)(22). Vicinal {110} faces generally replace {010} faces, which if present are usually small (16).…”

An estimate of dissolution rate constant of volcanic glass in volcanic ash soil from the Mt. Fuji area, central Japan

“…The order of elemental mobility obtained by the present study is roughly similar to but slightly different from that previously established for basalt weathering which is Ca > Na > Mg > Si > Al > K > Fe > Ti (Craig and Loughnan, 1964;Coleman, 1980;Smith et al, 1987). The possible causes for this difference are different volcanic glass/primary mineral content ratio, mineralogy and the effect of vegetation.…”

Hydrochemistry, weathering and weathering rates on Madeira island

“…Some studies have zoomed in on the transformation of primary into secondary phases during various stages of weathering on a microscopic scale. Examples can be found in Colman (1982), Eggleton and Smith (1983), Smith et al (1987), Banfield et al (1990), Wasklewicz (1994), and Berner and Cochran (1998). Another approach is to use the chemistry of water to determine the mobility and fluxes of elements in drainage of basaltic terrain, based on which denudation rates and CO 2 consumption can be estimated.…”