The role of grain size and porosity in the piezoelectric and elastic properties of SiO2-based materials was investigated using resonant piezoelectric spectroscopy, RPS, and resonant ultrasound spectroscopy, RUS. RPS performed on agate revealed a piezoelectric effect comparable in magnitude to that in single crystal quartz. The observed strong piezoelectricity in agate requires preferential orientation of SiO2 during crystal growth. Similarly, in novaculite and sandstone finite (but weak) RPS signals were evident, suggesting that the expected randomization of the piezoelectric quartz grains is incomplete. On the other hand, Vycor, a silica glass with a porosity of 40%, showed no evidence of the piezoelectric effect. According to temperature dependent RPS and RUS measurements, the α-β transition temperature in quartz does not change in polycrystalline samples. Finally, the temperature dependence under heating of the elastic constants is reversible in quartz and agate and irreversible in sandstone and vycor.RUS facilities in Cambridge were established through grant no. NE/B505738/1 to MAC from the Natural Environment Research Council. EKHS is grateful to the Leverhulme Foundation (RPG-2012-564) and EPSRC (EP/K009702/1) for financial support.This is the final version. It was first published by De Gruyter at http://www.degruyter.com/view/j/ammin.2015.100.issue-5-6/am-2015-5180ccby/am-2015-5180ccby.xm
