1) Volcanic rock 
Vitrophyre is a volcanic rock with larger crystals (phenocrysts) embedded in a glassy groundmass. Volcanic rock is formed when molten rock (magma), which is produced by a volcano, has cooled and solidified (crystallized). Groundmass of rock is the fine-grained mass of material in which larger grains or crystals are embedded. ...
(from the article `igneous rock`) ...rapidly, and congealed to form a finer-grained or glassy groundmass. A porphyritic volcanic rock with a glassy groundmass is described as having a ...
vitrophyre Any porphyritic igneous rock having a pronounced glassy groundmass; glass porphry.