The whole of the upper part of the cone consists of grey highly acidic lava.
An oxide may be both acidic and basic, i.e.
Quartz occurs as a primary and essential constituent of igneous rocks of acidic composition such as granite, quartz-porphyry and rhyolite, being embedded in these either as irregularly shaped masses or as porphyritic crystals.
The doctor turned red at her acidic tone and glanced at his chart.
It has also feebly acidic properties, forming ferrites with strong bases.