Bayerite polymorphs

The synthetic form of Al(OH)3, aluminium hydroxide (q.v.), is often encountered as a lake substrate. In such a context, die bayerite polymorph is usually precipitated however, Greenwood and Earnshaw (1999) indicate that precipitation from warm alkaline solutions can result in the preferential formation of gibbsite. 

Gibbsite Al(OH)3 AM 49 819 (1964) polymorphs bayerite, doyleite, nordstran-dite... 

At least seven different crystaUine phases of alumina hydrates are known (Table 3.1) (4—6). Among them are four polymorphs of the trihydroxide A1(0H)3 and two polymorphs of the oxyhydroxide AlOOH. The four trihydroxides are bayerite (7,8), usually denoted as a-Al(OH)3, gibbsite (8,9), usually denoted as Y-Al(OH)3, and the less common doyleite (10,11), and nordstrandite (12). Their structures are closely related. While characterization of bayerite and gibbsite has been the subject of many investigations, details on the structure of nordstrandite and doyleite are scarce. The availability of refined theoretical methods and computational power and the combination of the respective results with diffraction and vibrational spectroscopic data recently led to reanalysis of the structure of all of these... 

There are three polymorphs of aluminium trihydroxide gibbsite, bayerite and nordstrandite. The difference between the three polymorphs is in the stacking order... 

The transition aluminas contain varying amount of hydroxyl ions and are not well defined stoichiometrically therefore, they cannot be considered as true polymorphs of alumina. The structures of the forms occurring at a given temperature range are determined by the structure of the starting materials, and they are different for gibbsite, bayerite, boehmite, or diaspore. The microcrystalline state of these substances and the poor character of their X-ray diffraction pattern preclude the application of refined methods of structure determination. 

Bayerite is a rare white aluminium hydroxide mineral with composition Al(OH)3, the t) locality for which is Halrurium, Israel. It is one of the series of potymorphs of the Al(OH)3 system which includes gibbsite, doyleite and nordstrandite (qq.v.-, Chao et al., 1985). Bayerite is the polymorph which generally forms when Al(OH)3 is precipitated in solution, such as in lake formation. Bayerite is therefore to be expected in a pigment... 

Doyleite is a triclinic aluminium hydroxide mineral with composition Al(OH)3. It occurs as masses of soft white tabular crystals with pearly lustre which form from the weathering of aluminium-rich rocks in tropical climates. Hence, doyleite is often found in bauxites (. v.). Doyleite is closely related to another triclinic form of A1(0H)3, nordstrandite, and the monoclinic polymorphs, gibbsite and bayerite qq.v.), with which it may be found (Chao et al., 1985) it is also related to the orthorhombic dehydrated forms of AIO(OH), boehmite and diaspore qq.v.). Synthetic alu-minimn hydroxide Al(OH)3 is commonly encountered as a substrate for lake pigments. 

Gibbsite is a monochnic aluminium hydroxide mineral with composition Al(OH)3 (Megaw, 1934). It is named after the American mineral collector G. Gibbs (1776-1833) and was first described by Torrey in 1822. Gibbsite is also known as hydraigillite and is polymorphous with bayerite (monoclinic), doyleite... 

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