1. Tridymite can occur in seven crystalline forms.

2. The groundmass contains interstitial quartz or tridymite or cristobalite.

3. Minerals associated with this include quartz, cristobalite and tridymite, which may all be present in volcanic ash.

4. Compared to “normal” igneous rocks, this tridymite-hercynite rock has higher FeO, Al2O3, and lower SiO2 CaO, MgO, and alkalis (Na2O + K2O).

5. 25 The effect of addition of P_2O_5 in a few thousandths on the devitrification behavior of plate glass with primary phase of tridymite is different from that with primary phase of wollastonite.