Compositional variations in glauconite

Abstract

Variation in composition, Fe3+/Fe2+ ratio, per cent mixed-layering, and d(060) spacing have been determined both between and within grains of glauconite from the Folkestone Beds at 286.5 m in the Tollgate bore, Sandwich, Kent. Grains extracted from the rock were classified on the basis of size into large (> 1 mm) and small (< 1 mm), and on colour into light and dark green. Large grains have a progressive increase in Fe3+/Fe2+ ratio with increase in total iron, while small grains have variable ratios; the largest variation is in the dark grains. The effect of the range of Fe3+/Fe2+ ratio variations on structural formula (e.g. R3+) is discussed. The per cent mixed-layering is not related to colour. There is a greater variation in Al, Fe, and K contents in and between large grains than small grains. Both sizes of grains may be separated on d(060) spacings determined by X-ray diffraction. Glauconite from coral and gastropod casts has different d(060) spacings than that from bryozoan casts and variegated grains, but is similar to the small grains. Large light grains may have developed from small light grains but it is unlikely that the large dark grains developed from small dark grains. The large grains probably all formed under similar conditions, with a common origin; the small from several sources or from a single source under a variety of conditions.

Integrated diagenetic and sequence stratigraphy of a late Oligocene–early Miocene, mixed-sediment platform (Austral Basin, southern Patagonia): Resolving base-level and paleoceanographic changes, and paleoaquifer characteristics

“…Cryptocrystalline greenish grains (i.e., light and dark green, and brownish green) are interpreted to be autochthonous glaucony according to their: (1) irregular rounded granular micromorphology (Amorosi, 1997); (2) geochemistry (Supplemental Table S2), when compared to glaucony in a variety of depositional environments (Takahashi, 1939;Hendricks and Ross, 1941;Burst, 1958;Buckley et al, 1984;Longuépée and Cousineau, 2006;Eder et al, 2007;Sánchez-Navas et al, 2008); (3) petrographic attributes, including microfractures (Sánchez-Navas et al, 2008); and, (4) crystal lattice inter-element correlations (Fig. 8, Supplemental Table S3; Ireland et al, 1983;Longuépée and Cousineau, 2006).…”

The unknown planktonic foraminiferal pioneer Henry A. Buckley and his collection at The Natural History Museum, London

“…Buckley described a new species (Globorotalia oveyi Buckley, 1973) and used the collection in a series of papers on climate change, glaciation and sapropel formation (Buckley 1976;Buckley et al 1982;Buckley & Johnson 1988). Buckley also published on the formation of minerals, such as glauconite (Buckley et al 1978(Buckley et al , 1984Fleet et al 1980;Hall & Buckley 1991), and the mineralogical composition of sediments (Buckley et al 1974;Easton & Buckley 1979, 1983Buckley & Woolley 1990). Despite early encouragement from Dr Wiseman, Buckley was officially discouraged by his later managers at the NHMUK from working on the biology and taxonomy of planktonic foraminifera for a number of political reasons, and because he was not considered to be a trained micropalaeontologist (Whittaker, pers.…”