Is silicon oxide=rock?
You ask:


  Are common rocks (e.g. rock from mountains or rivers, bricks, or even concrete) actually silicon oxides? Or it is just one of compositions?


Rocks can contain silicon oxides, but that's not part of what the definition of a "rock" implies. From an introductory course in geology at the University of Texas at Austin, a rock is defined as:


  Any coherent, naturally occurring substance generally composed of minerals.


That's all there is to it. Whether or not the minerals include silicon oxides has nothing to do with a rock being called a rock.