Chemical changes induced in aragonite using treatments for the destruction of organic material

Abstract

Treatments used to destroy or remove organic material prior to chemical analyses of carbonate material alter the elemental composition of aragonite. To assess chemical changes in aragonite caused by various treatments, an abiogenic aragonite crystal was powdered and split into five groups. One group was left untreated as the control group. The four remaining groups were treated as follows: (1) soaking in a 5% sodium hypochlorite solution for 24 hr.; (2) boiling for 3 min. in a 5 N sodium hydroxide solution; (3) soaking in a 30% hydrogen peroxide solution for 24 hr.; and (4) heating for 2 hr. at 400°C. Each group was split subsequently and analyzed for Ca, Sr, Mg, Mn, Fe, Na and K content. Using a statistical technique designed specifically for compositional data, analyses indicate that all of the treatments except heating caused significant changes in the composition of the aragonite. Although the extent of the chemical alteration differs according to the particular treatment, broadly similar changes occurred in all chemically treated samples. Most notable are decreases in Fe and Mg, possibly related to their occurrence in the aragonite as adsorbed ions, as interstitial ions, or in structural defect sites. The significant changes caused by these chemical treatments can lead to misinterpretations of laboratory-altered chemical compositions as products of natural processes.