Zincalstibite-9<i>R</i>: the first nine-layer polytype with the layered double hydroxide structure-type

Abstract

Abstract Zincalstibite-9 R , a new polytype in the hydrotalcite supergroup is reported from the Monte Avanza mine, Italy. It occurs as pale blue curved disc-like tablets flattened on {001} intergrown to form rosettes typically less than 50 μm in diameter, with cyanophyllite and linarite in cavities in baryte. Zincalstibite-9 R is uniaxial (–), with refractive indices ω = 1.647(2) and ε = 1.626(2) measured in white light. The empirical formula (based on 12 OH groups) is (Zn 1.09 2+ Cu 0.87 2+ Al 0.04 ) Σ2.00 Al 1.01 (Sb 0.97 5+ Si 0.02 ) Σ0.99 (OH) 12 , and the ideal formula is (Zn,Cu) 2 Al(OH) 6 [Sb(OH) 6 ]. Zincalstibite-9 R crystallizes in space group R , with a = 5.340(2), c = 88.01(2) Å, V = 2173.70(15) Å 3 and Z = 9. The crystal structure was refined to R 1 = 0.0931 for 370 unique reflections [ F o &gt; 4σ( F )] and R 1 = 0.0944 for all 381 unique reflections. It has the longest periodic layer stacking sequence for a layered double hydroxide compound reported to date.