1. There are few rulings regarding stones. Not every stone could be used for prostration.Sajdah can be performed on limestone & gypsum, but the recommended precaution is that Sajdah should not be optionally performed on baked gypsum, lime, brick & baked earthenware, etc.
3. If a person does not possess anything on which it is allowed to perform Sajdah, or, even if he possesses such a thing, he cannot perform Sajdah on it due to severe heat or cold, he should perform Sajdah on asphalt or tar, and if that is not possible, on his dress or the back of his hand, or on any thing on which it is not permissible to perform Sajdah optionally. However, in such a situation, the recommended precaution is that as long as it is possible to perform Sajdah on his dress he should not do Sajdah on any other thing.
4. One can prostrate on wood but it shouln't be polished or painted. The criterion is there shouldn't be a layer on wood.
5. As per (3)
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