Mourning Jewelry is jewelry worn after the loss of a loved one.  At one point it was given out by wealthier families after a death.

Mourning Jewelry is typically made of jet, ebony, onyx, or bog oak.   In many instances hair is woven into it, or there is a compartment to hold a lock of hair or photo.  Sometimes these are hidden compartments.   Above you see a lovely piece of mourning jewelry.  What a lovely custom! I am surprised it fell out of fashion.