*Mineralogy of Peralkaline Silicic Volcanics: Information from Kone Volcano, Ethiopian Rift Valley DOI: http://dx.doi.org/10.5772/intechopen.102677*

Phenocryst compositions of Kone silicic volcanics are reported in **Tables 1**–**4**. Compositions of alkali feldspar span the anorthoclase-sanidine boundary (**Figure 3a**). There is no notable compositional variation between individual samples (**Table 1**). Zoning is uncommon. Where present is usually normal, whereby the rim is richer in K2O than the core (**Table 1**). Microlites of alkali feldspar have slightly more potassic composition than the alkali feldspar phenocrysts. It is noteworthy that analyses of alkali feldspar matrix are broadly comparable to those of alkali feldspar phenocryst rim. Clinopyroxene is generally hedenbergite (**Figure 3b**). Hedenbergite is essentially unzoned (**Table 2**). Aenigmatite shows very restricted variation in TiO2, FeO and Na2O (**Table 3**). Olivine appears almost pure fayalite and


**Table 2.**

*Composition of clinopyroxene in Kone silicic volcanics.*

### *Mineralogy*


### **Table 3.**

*Compositions of aenigmatite from Kone silicic eruptives.*

has a high content of MnO (4.33 wt.%, **Table 4**), which is a characteristic feature of peralkaline rhyolites [16]. Fe-Ti oxides are essentially ilmenite (**Table 4**). It is noteworthy that similar phenocryst and groundmass mineralogies occur.

Matrix glass has a rhyolite composition with SiO2 content of 69.3 wt.% (**Table 4**). It has high K2O content (5.7 wt.%), but extremely low Na2O content (2.6 wt.%). The low Na2O content may be due to deutric mobilization.

*Mineralogy of Peralkaline Silicic Volcanics: Information from Kone Volcano, Ethiopian Rift Valley DOI: http://dx.doi.org/10.5772/intechopen.102677*


**Table 4.**

*Compositions of olivine, ilmenite, apatite and glass matric in Kone silicic eruptives.*
