Unraveling the atomic structure of biogenic silica: evidence of the structural association of Al and Si in diatom frustules

Microbial mediation of benthic biogenic silica dissolution

“…The low water depths and shallow OPDs of the type III profiles in the Guinea and Angola basins substantiate the possibility that these locations may be supplied with more labile OM, and support considerable anaerobic mineralization providing significant amounts of reduced chemical species. Moreover, the type III locations all lie in areas of enhanced terrigenous input; hence, reduced BSi solubility (due to incorporated traces of Al) which would also cause deviating kinetics (Dixit et al, 2001;Romero and Hensen, 2002;Gehlen et al, 2002). For the data presented, BSi solubility increases with water depth in the Argentine Basin, which may reflect decreasing terrigenous impact further offshore.…”

Possible mechanism of structural incorporation of Al into diatomite during the deposition process I. Via a condensation reaction of hydroxyl groups

“…Because the existence of Al in the structure of diatomite is demonstrated to effectively lower the solubility of diatomaceous silica and is beneficial to the preservation of diatomite [13][14][15][16][17], many studies focus on the properties of structural Al in diatomite, such as its content and coordination number (tetrahedral or octahedral coordination) [18][19][20][21][22]. In addition, researchers have estimated the transport of Al from the oceans' surface to the sediment [23][24][25] by studying the structural Al in diatomite. This is an effective estimator because the Al/Si ratio can be as high as 0.16 [14,15,26], and the diatomaceous earth form is the most abundant form of silica on earth [27].…”

The formation of metastable aluminosilicates in the Al–Si–H2O system: Results from solution chemistry and solid-state NMR spectroscopy

“…The dashed lines are provided for the minerals to guide the eye. Sample IDs correspond to those presented in Table 3. incorporated in biogenic silica (Gehlen et al, 2002). We must stress, however, that given the breadth of the lines observed in this study it is likely the above structural parameters represent average values, and that there exist a wide distribution of bond lengths and angles typifying an amorphous phase.…”

“…Allophane-like phases have also been implicated in controlling the bioavailability of Al (Doucet et al, 2001;Exley et al, 2002). Al [4] containing aluminosilicate phases have been identified as the dominant phases in hydrothermal scales (Gallup, 1997;Nishida et al, 2009) siliceous hot spring deposits (Yokoyama et al, 2004), biogenic silica (Gehlen et al, 2002), and inorganic opals (Brown et al, 2003;Paris et al, 2007). Houston et al (2008) indicated that metastable Al [4] dominant aluminosilicate phases form during uptake experiments performed at pH >5 and higher dissolved silica concentrations despite thermodynamic forces driving the formation of kaolinite.…”