On Li-bearing micas: estimating Li from electron microprobe analyses and an improved diagram for graphical representation

Abstract

Lithium may constitute an essential element in micas, yet it cannot be detected by the electron microprobe. Since Li is critical for correctly classifying micas and properly calculating their formulae, several methods have been proposed to overcome this analytical deficiency. We offer empirical relationships between Li2O and SiO2, MgO, F, and Rb in trioctahedral micas, and between Li2O and F as well as Rb in dioctahedral micas. The resultant regression equations enable lithium contents to be sufficiently well estimated from EPM analyses within the range of validity discussed.Secondly, we introduce an easy to handle, new diagram with the axis variables [Mg-Li] and [Fetot + Mn + Ti-AlVI] for graphical representation and discuss its scientific rationale. Being based on absolute abundances of cations in the octahedral layer, the diagram provides a simple means to classify micas in terms of composition and octahedral site occupancy, and it also allows compositional relationships between Li-bearing and Li-free mica varieties as well as between trioctahedral and dioctahedral micas to be displayed on a single, two-dimensional diagram.

The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England

“…Stone et al, 1988;Henderson and Martin, 1989). The mica formulas have been calculated to 22 oxygen atoms and the Li 2 O content calculated according to Tischendorf et al (1997). All biotites are trioctahedral, consistent with the previous studies of Stone et al (1988), as the octahedral Y-site always contains more than 5 atoms per 11 oxygen atoms and the interlayer cation site atoms have a total of approximately 2.…”

The Paleoproterozoic metaconglomerate-hosted Castelo de Sonhos gold deposit, Tapajós Gold Province, Amazonian Craton: a modified paleoplacer origin

“…15A) and of Tischendorf et al (1997 - figure not included). A biotite substitution trend is also defined by the composition (Fig.…”

Mineral chemistry of barium- and titanium-bearing biotites in calc-alkaline volcanic rocks from the Mezitler area (Balikesir-Dursunbey), western Turkey.

“…It is difficult do assign a unique substitution mechanism for barium-and titanium-bearing micas because of the complexity of potential substi- Tischendorf et al (1997).…”

“…Micas are classified as Fe-and Mg-biotites on the classification diagram (Fig. 3b) proposed by Tischendorf et al (1997) Table 2). (Yavuz, 1999) and Pyrox (Yavuz, 2001b) softwares were used for calculations of amphibole and pyroxene samples.…”

“…(Rieder, 2001 (Yavuz and Öztas, 1997). Mica variety is identified on the classification scheme by Tischendorf et al (1997) using the Limica (Yavuz, 2001a) Table 2 and in Table 3, respectively. The BIOTERM (Yavuz and Öztas, 1997), LIMICA (Yavuz, 2001a) and MICA + (2002) computer programs are used for mineralogical calculations of the mica analyses.…”