Prostrating on carpet, allowed?

Synopsis: The popular Shia view is that the prostration in prayer is only valid if the forehead is placed on bare earth, or on something that grows from the earth, as long as it is not edible or wearable (source). This post briefly examines if it is permissible to prostrate on other items (such as carpets etc) as well. Nevertheless, this post is only meant to serve an academic purpose, and readers are advised to refer to their own trusted scholars (marja, mufti etc) for their individual practices.

"The lexicon of reliable narrations from the Prophet and the Imams (as)" by Ayatullah Asif Muhsini, Volume 5 Page 39 (Original Arabic page posted at the bottom of the post)

Items on which prostration is valid, and the ones on which it is invalid:

(From the book 'Man la yahdaruhul faqih'): Hisham b. al Hakam asked Imam Ja'far al Sadiq (as): 'Please inform me of the items on which it is permissible to prostrate, and the ones on which it is impermissible?' Imam al Sadiq (as) replied: 'Prostration is only permissible on the earth, or that which grows from the earth, except which is an edible or wearable.' So Hisham asked further: 'May I be your ransom, but why is that?' Imam (as) replied: 'Prostration is submission to Allah, so it should not be performed on edibles and wearables, as materialistic people [almost] worship edibles and wearables. As the prostrator is engaged in the worship of Allah, he should not place his forehead on those items of worship of materialistic people on which they take pride. Prostration on the earth is best, as it is the ultimate form of humbleness and submission to Allah.'

I (Ayatullah Asif Muhsini) say: At best this proves [prostration on other than the earth, or what grows from it apart from the edibles and wearables] it to be just makrooh (disliked).

"Tabsiratul fuqaha" by Ayatullah Sadqi al Tehrani, Page 109 (Arabic page at bottom)

Prostration is only permissible on earth or that which grows from it, apart from the edibles and wearables such as on a ring, shoe or sock etc. It is allowed though on items which have transformed from being edibles or wearables, such as on the ashes of an edible or wearable, or that which is made from a wearable and cannot be reverted back to its wearable form such as a carpet made from wool or cotton as it is not possible to take apart its threads and transform it back to a wearable form. Among the conditions of impermissibility of prostration is the item being actually a wearable item, same as with the condition of impermissibility on edibles, except if it is argued [for the sake of it] that even the derivatives of edibles and wearables are counted among them. Anyhow, there is unconditionally no issue with prostrating [on such derivatives] apart from the actual edibles and wearables.

"Muj'am al ahadith al mu'tbarah" by Ayt Asif Muhsini, vol 5 p39