Another basic indium sulfate InOHSO4 with rhombohedral crystals is made by heating an indium sulfate solution at 160 °C or over for about a week in a sealed tube. This insoluble basic salt also forms if indium sulfate solution is diluted below 0.005 molar. So a precipitate forms from diluted solutions as well as from heated solutions. Anhydrous double sulfates Two different types of anhydrous double indium sulfates have been made. One is from the family MMIII(XO4)3, with MI being a large singly positive ion such as K, Rb, Cs, Tl or NH3; MIII is triply charged and can be Al, Ga, In, Tl, V, Cr, Fe, Sc and other rare earths; and X is S or Se. Most of these have a rhombohedral crystal structure. However, triammonium indium trisulfate, (NH4)3In(SO4)3 converts from rhombohedral to monoclinic as the temperature drops below 80 °C, and converts back into a rhombohedral form with space group R3c as the temperature rises above 110 °C. The low temperature monoclinic form has space group P21/c, a=8.96, b=15.64 c=9.13 β=108.28° Z=4 The high temperature form is termed "β-". An explanation for this transition is that ammonium (and also thallium) is a non-spherical ion and thus has lower symmetry. However, when it is heated enough, dynamical disorder causing random orientations makes the ions on average spherically symmetric. Alkali metal ions are spherical in shape at all temperatures and form rhombohedral structures. Double sulfates of this form exist of indium with the alkali metals sodium, potassium, rubidium, and cesium. These can be formed by heating a solid mixture of the individual sulfates to 350 °C. Another series of anhydrous rhombohedral double salts in the same series of TlFe(SO4)2 exists. These can be made by heating a mixture of anhydrous sulfates at 350 °C, or by dehydrating hydrous double alum type salts at 300 °C. The substances in this series are RbIn(SO4)2, CsIn(SO4)2, TlIn(SO4)2 and NH4In(SO4)2. Although KIn(SO4)2 exists it has a different crystalline form. Hydrated double sulfates Hydrated double salts of indium in an alum structure exist with formula MIIn(SO4)2·12H2O. All alums have a cubic crystal structure with space group Pa3. The indium cesium alum CsIn(SO4)2•12H2O has formula weight 656.0, unit cell width 12.54 Å, cell volume 1972 Å3 and density 2.20 g/cm3. It has the β alum structure. The cesium alum can be used in the analysis of indium. It precipitates when cesium nitrate is added to