My dad was blessed to get to meet many people in his news career, and among those were Pope St. John Paul II and St. Mother Teresa. When he was with St. Mother Teresa, he received a widow’s mite from her. Since she touched it, does it qualify as a third - class relic? If so, I am having a hard time finding a reliquary small enough for it. My dad is not religious in the typical sense, but he loves Mother Teresa and Pope JPII, and is supportive of my faith.
I have no idea what class of relic that would make it, but it’s wonderful that you have a personal gift from a Saint that’s been handed down to you. Maybe try doing a Google Images search using the the phrase “Making a necklace out of a widow’s mite.”
An Internet search revealed that Eastern Christian Supply Company sells some small metal reliquaries, link.
If you are looking for something less expensive, The Coin Supply Store sells some acrylic coin holders, link.
Amazon also has some inexpensive very attractive reliquaries: amazon.com/s/ref=sr_nr_n_11?fst=as%3Aoff&rh=n%3A1055398%2Ck%3Areliquary&keywords=reliquary&ie=UTF8&qid=1475810953&rnid=2941120011
A priest friend told me about the ones on Amazon.
If she was alive and gave it to him it is not a relic of any kind.
However, it is an item to be treasured.