pyromeride

from The Century Dictionary.

• noun In petrography, a somewhat altered spherulitic quartz-porphyry or rhyolite (Monteiro). This name, first applied by Haüy to the orbicular diorite of Corsica (corsite or napoleonite), was given because it was thought that only a part of the minerals in the rock was fusible, quartz being at that time considered infusible.