all that you have said is **wrong and incoherent**. 
We do not pray on any "material". the only material we pray on is  mud that is pure and clean. We don't pray on clay to "worship it", we pray on it because it is pure, and as all muslims-shia and sunni- believe that one must be clean and in a clean environment to pray. 

I once asked my Sunni friend: *"why do you Sunni people pray with your shoes on in the mosque? isn't the mosque an untainted and a holy place? what if you get mud on shoes, can you still pray with them?"* 
she replied with: *" yes we can pray with our shoes if there's mud on it because mud is 'tahr' so it doesn't really matter"*
I told her that *" us Shia Muslims pray on mud merely because its 'tahr' and Sunni Muslims object that and believe that we are worshiping them as idols"*
And of coarse **she had nothing to reply.** 

the point is that us Shia Muslims pray on a 'turbah' (which comes from the word tarab that means mud) because it is tahr and pure. And the prophet used to pray on pure flat **GROUND**  because in the  prophets time they did not have a sijadah as there was no technology back then to produce them.