Answer
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:
It is permissible for women to wear rings of gold or silver with diamonds or other precious stones such as emeralds, rubies and carnelians, or of iron if they wish.
In responding to your question, the Fatwa Center at Islam Q and A, states:
Wearing jewelry in Islam
It is permissible for women to wear rings of gold or silver with diamonds or other precious stones such as emeralds, rubies and carnelians, or of iron if they wish. The basic principle is that wearing jewelry by women is permissible and there is no text to suggest that any of that is not allowed.
It is not disliked to wear a ring of iron.
Extravagance in wearing Jewelry
Imam Ibn Qudamah (may Allah have mercy on him) said:
“It is permissible for women to wear jewelry of gold, silver and gemstones according to their customs and traditions, such as bangles, anklets, earrings and rings, and what they wear on their faces and on their necks, arms, feet, ears and so on.” (Al-Mughni, 2/324)
It is stipulated that there should be no extravagance in wearing these things.
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Imam An-Nawawi (may Allah have mercy on him) said:
“Our companions said: All kinds of jewelry are permissible for women; it is only permissible so long as there is no obvious extravagance involved.” (Al-Majmu`, 5/523)
Almighty Allah knows best.
Source: www.islamqa.info