Good Morning Shelly, we are flying blind without an image. As we are currently inundated with questions on Help Central, unfortunately we can only assign a certain amount of time, gratis, for each question, in fairness to other visitors.
You might consider, getting an Expert Appraisal carried out, that way you will have expert information about your necklace and will also know the value.
Images will be necessary. Clean the area around the mark. You might be able to see the mark more clearly now. Macro settings are important. Some visitors, tell me, they photograph their marks, with lens of camera, pointing through a magnifying glass. You might need assistance, but if the mark is that tiny, it will have to be enlarged in some way.
Another alternative, draw the mark on a piece of white paper and photograph your drawing of the mark. Every detail is important to include, including the shape of the surround (if any).
