Abstract: Unit-cell parameters of synthesized members of the crandallite (a = 7.007 Å, c = 16.216 Å)-goyazite (a = 7.013 Å, c = 16.650 Å) series vary linearly with composition between end-members. Most members of the series consist of 0.1 μm platy crystals, but crandallite also contains some larger (1–5 µm) tapered crystals elongated along the c axis.
With increasing Sr substitution the dehydroxylation temperature decreases from c. 475 °C for crandallite to 420 °C at 20 mole % Sr, and then increases to 440 °C for goyazite. Partial dehydroxylation of crandallite is accompanied by contraction of the c unit cell parameter and expansion of a, thereby retaining an unaltered unit cell volume. The much greater sensitivity of c to both Sr substitution and dehydroxylation may be due to the rigidity of continuous sheets of Al(OH)4O2 octahedra which are parallel to the (001) plane in these minerals.