The grainy reference is not to silicon or sand, it is to sound. A picture can also be grainy but there is no sand.
Transistor amps are referred to as sand amps due to the use of silicon. It is only incidental that they also sound 'grainy' for want of a better word that avoids any reference to the material used.
Transistor amps are referred to as sand amps due to the use of silicon. It is only incidental that they also sound 'grainy' for want of a better word that avoids any reference to the material used.