On my travels, I'm yet to see a minaret be used for auxiliary purposes. This is what they often look like:
This is the Hassan II Mosque in Casablanca, Morocco. It would be possible to add a clockface to the minaret, or turn it into a lighthouse (the Hassan II Mosque is on the beach), in order to give it additional functionality. However, I have never seen this happen in practice.
Question: Can a minaret have auxiliary functionality, such as also being a clock tower or lighthouse?
Here I use "can" as shorthand for "is it Islamically permissible" (I'm not asking "is it physically possible").
