Barium (Ba) is an important element in chemostratigraphy, but what are the element-mineral links of Ba?
Barium (symbol Ba; atomic number 56; relative atomic mass 137.327) [Link to Ba @ webelements.com]
Ba has one oxidation state, +2.
Barium is present in seven naturally occurring isotopes (130Ba, 132Ba, 134Ba, 135Ba, 136Ba, 137Ba, and 138Ba), of which 138Ba is the most abundant one.
Ba is a common a substitution for K; due to similar ionic radii (Ba2+ = 215 pm and K+ = 220 pm).
In geochemical analysis, barium is commonly reported in its element form in parts per million [ppm], though sometimes reported as an oxide, BaO, in weight percent [wt. % or %].
Common element-mineral links of Ba
The most common element-mineral links of Ba: barite (BaSO4) as the principal Ba mineral, K-feldspar, and mica through substitutions of K.
Ba in siliciclastic rocks
Ba occurs mostly in K-feldspar and K-bearing mica, such as illite, through the substitution of K+. However, Ba can also be present in plagioclase, as well as in amphibole and pyroxene, in apatite and calcite, due to the substitution of Ca2+. Ba may also be adsorbed on clay minerals and Fe and Mn oxides and hydroxides.
Good to know …
Barite as a drilling fluid additive
Barite is a common additive to drilling fluids (drilling mud) to increase the density of the fluid. Barite is a heavy mineral with a density of 3.51 g/cm3. Therefore, high concentrations (several thousand ppm), for instance in cuttings samples, may indicate contamination with drilling additives. In XRF analyses, high Ba concentrations may have a secondary effect (e.g. peak overlaps or secondary excitations) on other elements; often Ti is affected.
Ba in carbonate rocks
In carbonates, Ba concentrations are commonly very low. However, Ba can (together with Sr) substitute for Ca2+ and Mg2+ in carbonate minerals.
Ba in igneous rocks
In igneous rocks, a general increase of Ba with increasing Si content, i.e. from mafic to felsic, is common. For instance, ultramafic rocks usually have < 1 ppm Ba, basaltic rocks around 300-350 ppm, granitic rocks 400-850 ppm, and syenites up to 1600 ppm Ba. As mentioned above, Ba is a common substitute for K in K-feldspar, and for Ca in amphibole and pyroxene.