In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
Men are allowed to wear stones in their rings provided the stones do not fall under the category of unnecessary wastage.
Responding to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
Men are allowed to wear stones in their rings provided the stones do not fall under the category of unnecessary wastage. This would be the case if a person spends an extravagant amount of money on a stone while his neighbors cannot even have a decent meal. Wastage is forbidden in Islam. The Quran characterizes the wasteful as “the friends of Satan” (Al-Isra’ 17: 27).
As for wearing stones as jewelry, it is considered as copying women, which is forbidden in Islam.
Regarding the question of the stone embedded in the Prophet’s ring, its color is reported to have been black with a streak of white. As mentioned in the sources, the Prophet Muhammad (peace be on him) wore a ring to serve the purpose of a seal. He did this after being told by his Companions that his letters to the foreign dignitaries would not be honored unless they were stamped with a seal.
Finally, let me categorically state that considering stones as possessing magical, divining, or protecting properties is blasphemous and rejected outright by the clear teachings of Islam.
In Islam, even the most precious of stones, namely the Black Stone (al-hajar al-aswad), has no such significance. The Caliph Umar wanted to eradicate from the minds of people any trace of such an association when he openly declared: “I am quite certain that you are only a stone and have no power to benefit or harm. If not for the fact that I saw the Prophet of Allah kissing you, I would not have bothered to do so.”
Almighty Allah knows best.