ABSTRACT
Some quaternary compounds are formed in the Al–H–O–P system. AlPO 4 ·2H 2 O is stable at 25°C (Jameson and Salmon 1954; Martin 1960; Sveshnikova 1960). This compound also exists as minerals variscite and metavariscite (Kniep and Mootz 1973; Bass and Sclar 1979; Duggan et al. 1990). Variscite crystallizes in the orthorhombic structure with the lattice parameters a = 982.3 ± 0.4, b = 856.2 ± 0.9, and c = 962.0 ± 0.5 pm (Onac et al. 2004) [a = 985, b = 955, and c = 850 pm and experimental and calculated densities of 2.5 and 2.61 g·cm−3, respectively (McConnell 1940); a = 983.1 and 990.2, b = 963.5 and 965.9, and c = 855.5 and 1718.0 pm and calculated densities of 2.58 and 2.50 g·cm−3 for two types of variscite (Salvador and Fayos 1972); a = 982.2 ± 0.3, b = 856.1 ± 0.3, and c = 963.0 ± 0.3 pm and a calculated density of 2.59 g·cm−3 (Kniep et al. 1977)].
