COMPARING DIRECT CARBONATE AND STANDARD GRAPHITE ¹⁴C DETERMINATIONS OF BIOGENIC CARBONATES

Phase transitions in biogenic amorphous calcium carbonate.

Crystalline biominerals do not resemble faceted crystals. Current explanations for this property involve formation via amorphous phases. Using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), here we examine forming spicules in embryos of Strongylocentrotus purpuratus sea urchins, and observe a sequence of three mineral phases: hydrated amo...

Nitrogen Determinations by Direct

All methods for the determination of urea in urine dependent on purely chemical processes for the hydrolysis of the urea are apparently destined to become antiquated, if not forgotten, because of the abundant supply of urease now available for such hydrolysis. It would be easy to devise an excellent direct Nesslerization method for the determination of urea in urine on the basis of the Folin-Pe...

Low-temperature magnetic properties of pelagic carbonates: Oxidation of biogenic magnetite and identification of magnetosome chains

[1] Pelagic marine carbonates provide important records of past environmental change. We carried out detailed low-temperature magnetic measurements on biogenic magnetite-bearing sediments from the Southern Ocean (Ocean Drilling Program (ODP) Holes 738B, 738C, 689D, and 690C) and on samples containing whole magnetotactic bacteria cells. We document a range of low-temperature magnetic properties,...

The Role of Carbonate Solvents on Lithium Intercalation into Graphite

Discussion of cathodoluminescence of Recent biogenic carbonates: an environmental and ontogenetic fingerprint

G. M. Friedman comments: Barbin et al. (1991) state 'most authors consider recent primary biogenic carbonates to be non-luminescent.' They quote several authors who have made such negative statements, but they do not reference studies that have demonstrated the usefulness of cathodoluminescence in the study of modern biogenic carbonates that make up reefs. Barbin et al. (1991) are not alone in ...