SWELL ING MINERALS IN A BASALT AND ITS WEATHERING PRODUCTS FROM MORVERN, SCOTLAND: II. SWELL ING CHLORITE

ABSTRACT: A swelling chlorite from unweathered basalt has been characterized by XRD, IR, DTA and chemical nalysis. Its 001 spacing of 14.9/ ~ increases to18.0 A on treatment with glycerol and decreases to 13.9 A (with a broad iffraction effect at 14-10/~) after heating to 550~ The mineral has an 060 spacing of 1.537/ ~ consistent with a trioctahedral composition, but its OH stretching band at 3638 cm- ldoes not show the expected pleochroism, suggesting ananomalous hydroxide sheet which chemical nalysis shows i incomplete. Although the mineral has a CEC of ~ 50 mEq/100 g, smectite is not present, but all the techniques show that he mineral has some saponitic haracter, indicating that it probably has a structure intermediate b tween swelling chlorite and saponite. The weathering of a Tertiary basalt at Killundine, Morvern, to a red residual rubble dominated by secondary clay formed from labradorite has been described by Bain et al. (1980). In part I of this study (Bain & Russell, 1980) interstratified montmorillonite-ver-miculite-illite, which is the main mineral in the weathered material, was characterized structurally and chemically, and this paper is devoted to a similar characterization f a swelling chlorite-type mineral which occurs in the fresh basalt