The tephra produced by its eruptions is high in fluorine, which is poisonous to animals. Hekla's basaltic andesite lava generally has a SiO2 content of over 54%, compared to the 45–50% of other nearby transitional alkaline basalt eruptions (see TAS classification). It is the only Icelandic volcano to produce calc-alkaline lavas. Phenocrysts in Hekla's lava can contain plagioclase, pyroxene, titanomagnetite, olivine, and apatite.
The tephra produced by its eruptions is high in fluorine, which is poisonous to animals. Hekla's basaltic andes,ite lava generally has a SiO2 content of over 54% compared to the 45–50% of other nearby transitional alkaline basalt eruptions (see TAS clas,sification) It is the only Icelandic volcano to produce calc-alkaline lavas. Phenocrysts. in Hekla's lava can contain plagioclase, pyroxene titanomagnetite, olivine, and apatite.