Layered structures, polyhedral sheets

The crystal structure of another borate mineral, garrelsite, NaBa3Si2B70i6(0H)4, has been determined. This structure has a three-dimensional framework of silicoborate sheets, and Ba—O polyhedral layers. The silicoborate sheets comprise a new type of silicoborate chain (with two types of alternating Si and B tetrahedral four-membered rings), the pentaborate anion B5O12, and octahedrally co-ordinated... 

Figure 2. Polyhedral representations of crystal structures ofMn oxide minerals with layer structures. (A) Lithiophorite. (B) Chalcophanite. (C) Na-rich bimessite-like phase showing disordered H20/Na (light color ball) sandwiched between the Mn octahedral sheets. Adapted from (8).

The carbon-arc plasma of extremely high temperatures and the presence of an electric field near the electrodes play important roles in the formation of nanotubes[ 1,2] and nanoparticles[3]. A nanoparticle is made up of concentric layers of closed graphitic sheets, leaving a nanoscale cavity in its center. Nanoparticles are also called nanopolyhedra because of their polyhedral shape, and are sometimes dubbed as nanoballs because of their hollow structure. 

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