The nature of kerolite, its relation to talc and stevensite

Abstract

SUMMARY. Kerolites from Goles Mountain (Yugoslavia), Wiry (Poland), Madison Co. (North Carolina), and Kremze (Czechoslovakia) are compared with talc and stevensite. Chemical analyses give a composition for kerolite near R3Si4010(OH)2.nH20 with R mainly Mg and n about 0.8-I.2. Infra-red data and dehydration-rehydration experiments suggest that the additional water is partly surface-held hydrogen-bonded molecular water, lost up to about 3oo ~ and easily recoverable, and 'water' held as surface hydroxyls, lost at temperatures up to about 65o ~ and less easily recoverable. The surface area of kerolite from North Carolina by nitrogen absorption measurements is 196 mZ/g. X-ray data show broad basal reflections, a basal spacing (after Lorentz-polarization correction) of about 9.6 J~ and a crystallite size of about five structural layers, which is consistent with the large surface area. Two-dimensional hk bands indicate a randomly stacked layer structure with b ~ 9"I 4 A and a crystallite 'diameter' of about r5o A. The basal spacing shows no expansion in water and no thermal contraction up to 50o ~ A partial and irregular swelling with ethylene glycol is obtained only after prolonged cxposure (several weeks). In both respects, kerolites differ from stevensite. Kerolites come close to talc in structure and composition but differ in having a highly random layer arrangement, a slightly enlarged basal spacing, which could be due to misfit of layers caused by random stacking, and weaker interlayer bonding.Kerolite is considered to be a useful varietal name for this talc-like mineral in agreement with the views of D'yakonov and of Maksimovic. It cannot be defined as serpentine + stevensite.THE name kerolite, suggested by Breithaupt (I823, p. 254 ) for a mineral of waxy appearance, was derived from the Greek KVpor (wax) and 2,~0o~ (stone). In English, two spellings have been commonly used, kerolite and cerolite; the former is preferred here because it appears to have priority and reflects more obviously the Greek origin of the word. The name has appeared in most of the major mineralogical texts but over the years has tended to become discredited owing to difficulties in obtaining an adequate definition and significant chemical formula; a useful survey has been given by Stoch (1974, pp. 286-8).Occurrence. Kerolite is commonly considered to be of low temperature origin; field evidence and the colloform texture support a deposition from colloidal suspension. It occurs generally in association with weathered ultramafic rocks as coatings and as veins filling cracks and often is intimately mixed with a poorly crystalline serpentine mineral. Maksimovic 0973) found that kerolite occurred at the bottom of a weathering profile in association with partially weathered and fresh rock. This description accords with our field observations, which indicate that kerolite is consistently found only where fresh or partially altered rock outcrops.Kerolite as a mineral species. Materials called kerolites are always extremely fine-grained and often ...

Bond Energy of Adsorbed and Interlayer Water: Kerolite Dehydration at Elevated Pressures

“…The kerolite used in this study was from Carter's Mine, Madison County, North Carolina, and was described by Brindley et al (1977). Individual crystallites are plates about 150/~ in diameter in plan.…”

“…They argued that the presence of H20 in the interlayer was not responsible for the increase in the basal spacing. Brindley et al (1977) found that weight loss due to dehydration was gradual between 110 ~ and 700~ The dehydration was completely reversible after heating to 300~ and 70-90% reversible after heating to 650~ On the basis of the gradual weight loss, its variable rehydration potential, and infrared (IR) data showing several frequencies attributed to molecular water and hydroxyl groups, they speculated that water in kerolite could reside in a number of locations, such as layer surfaces and edges. They suggested that most of the water was present as Copyright 9 1991, The Clay Minerals Society adsorbed molecular water and as surface hydroxyls, with a small amount possibly retained in the hexagonal tings of the tetrahedral sheet.…”

“…As noted by Brindley et al (1977), kerolite is distinguished from talc by the extreme disorder of the layer stacking and its greater ability to hold H20 molecules and OH ions at surface imperfections. This behavior is similar to that ofsmectite; however, the non-swelling behavior of kerolite offers the opportunity to study the effects of surface properties, without interference of an expanding interlayer region.…”

“…Eberl et al (1982) and Khoury et al (1982) described mixedlayer stevensite/kerolite that appeared to have precipitated from saline solutions and that was possibly a precursor in the secondary formation of sepiolite. Kerolite also occurs in weathering profiles of ultramafic igneous rocks (Maksimovi~, 1966;Brindley et aL, 1977). Brindley et al (1977) found the actual basal spacing of kerolite to be 9.65 A, after correction for Lorentzpolarization effects.…”

“…Kerolite also occurs in weathering profiles of ultramafic igneous rocks (Maksimovi~, 1966;Brindley et aL, 1977). Brindley et al (1977) found the actual basal spacing of kerolite to be 9.65 A, after correction for Lorentzpolarization effects. Most of the increase in the basal spacing compared with that of talc (9.38 /~) was attributed to disordered layer stacking, which produced less effective packing along Z*.…”