This sample of phonolitic welded ignimbrite comes from the Arico ignimbrite, Tenerife.
In thin section this pyroclastic rock contains fragments of alkali feldspar and biotite with minor magnetite, hornblende and diopside, flattened pumice clasts (fiamme) and lithic fragments in a matrix of recrystallized volcanic glass shards.
Mount Teide geology
Virtual microscope slides of thin sections
The Instituto de Astrofisica de Canarias Observatory del Teide is located on a ridge of a dormant volcano, about 2390 m above sea level on the island of Tenerife. Here are links to a couple of rock sections taken from this volcanic area.