Table 1. Summary of d spacings and transition parameters for samples investigated.

Lattice data are in ångström and temperatures are in kelvin. d(101)_α and d(111)_β are the d spacings for primary α- and β-cristobalite peaks, respectively. Δd _α is the thermal expansion of d(101)_α for the α phase prior to the onset of the α–β transition. Δd _α–β is the change in the d spacing during the transition following thermal expansion (Δd _α). T _tr is the transition temperature range for the α–β inversion detected by XRD and DSC.

Sample	Type	d(101)α 298 K	d(111)β 573 K	Δd α	Δd α–β	T tr (XRD)	T tr (DSC)
MBA5/6/99	Ash	4.064	4.124	0.014	0.046	443–483	448–508
MRA5/6/99	Ash	4.067	4.133	0.015	0.051	448–493	–
Hemenway	Standard	4.055	4.108	0.018	0.035	513–553	–
DKSmith	Standard	4.038	–	–	–	–	–
Talvitie	Isolate	4.057	–	–	–	–	–