The application of chemical staining to separate calcite and aragonite minerals for micro-scale isotopic analyses.

Abstract

Staining is a useful laboratory tool for distinguishing specific carbonate minerals from a mixture of carbonates. Feigl's and Meigen's solutions are commonly used to distinguish aragonite from other carbonates. Feigl's solution stains the aragonite surface black and Meigen's stains purple, whereas the coexisting calcite remains nochang in color with either solutions. Both methods were applied to an authigenically precipitated carbonate chimney and a recrystallized metamorphic marble. Meigen's solution was favorable to stain fine and euhedral aragonites, but not effective for recrystallized aragonites. Feigl's solution was applicable to identify both types of aragonites.As a sample that demonstrates application of the Meigen's solution, isotopic analyses were carried out on aragonite and calcite separated from the seepage carbonate chimney collected from the Conical seamount of the Mariana forearc.

Magnetic separation of calcite and aragonite for use in radioactive carbon analysis

“…Thereby entirely segregating amorphous phases are removed from the mixture of carbonates. Subsequent separation of aragonite and calcite used a similar procedure but with two type of staining conditions: (1) 15 minutes at 70 deg.C (Kato et al, 2003), and (2) 10 minutes at 80-90 deg.C. The first treatment stains aragonite purple, whereas the second treatment stains aragonite a dark purple although both treatments do not stain calcite; the second treatment was initially applied for periods up to 1 hour, but did not result in increased staining after that achieved within the first 10 minutes (Fig.…”

“…At first, we modified the 10% Meigen's solution staining method of Friedman (1959), Suzuki et al (1993) and Kato et al (2003) for the separation of amorphous and carbonate material by using an approach where samples of each grain size were stained for 10 minutes at 55 deg.C. Amorphous phases were stained pink, whereas aragonite and calcite remained white, meaning that amorphous grains are coated by cobalt nitrate and, as such, became magnetic.…”

Oxygen isotopes in Molluscan shell: Applications in environmental archaeology

“…They removed the outer calcite layer with a manual drill, and then samples were drilled from the last-deposited growth increments. Postsampling, the shells were checked for diagenesis by XRD and by staining with Feigl's solution (Kato et al 2003).…”

A New Radiocarbon Pretreatment Method for Molluscan Shell Using Density Fractionation of Carbonates in Bromoform

“…The method of heavy liquid density fractionation has been said to be "laborious and inappropriate for precise microscale sampling," though with no substantiation (Kato et al 2003). We have therefore pursued and developed an effective carbonate density separation method for the separation and isolation of molluscan shell aragonite from calcite using bromoform.…”

“…Molluscan shells are mostly comprised of calcium carbonate, though this compound may exist in different crystal structures, or polymorphs (Kato et al 2003). There are 3 polymorphs of calcium carbonate; calcite and aragonite are the most common (Falini et al 1996).…”