Siloxane condensation mechanism

I want to formulate the condensation reaction mechanism for the formation of siloxane links. 


[![Siloxane formation](https://i.stack.imgur.com/yPl8g.png)](https://i.stack.imgur.com/yPl8g.png)


I don't see how to express it as an addition-elimination reaction, because even though the silicone atom is positively polarized, it cannot form a fifth bond that would result from a nucleophilic attack by the other silanol. Is it a concerted reaction? 


Any input is helpful, so no limit on conditions. 


Any key publications? 


