Hi Courtney,
Welcome to Pearl-Guide!
I'm going to copy and past from the sticky thread at the top of this forum; note especially that a
white background is much better when trying to assess pearls. A black background just swallows up details and luster.
Welcome to Pearl-Guide!
If this is your first post, please be patient-- your post and photos will need to be approved by a moderator before they can appear on the forum. 
Feel free to post your own thread in this section, but please be sure to answer the following questions in your thread!
We would be pleased to try to help you determine what sort of pearls you have, but we will need some information from you first.
We need you to answer every question:
1. Do the pearls feel slightly gritty or smooth when rubbed gently against another pearl (or against the edge of your tooth, if there is only one pearl?) Please rub gently!
If they are gritty, they are likely to be real nacre (genuine pearls.) If they feel smooth, they are likely imitation pearls.
2. Please provide clear, in-focus photos without flash against a white background (a paper towel works nicely.)
Include close-ups of the clasp (front and back) and a few of the pearls. If there are flaws, include a photo of those. Also the box they came in, and tags if you have them.
3. Any history you can give us about the pearls. Where/when you or your relative got them, any documentation you have (receipts, appraisals), their price range if you know it, etc.
4. Describe any marks on the clasp. These may be numbers (14K, 585, 750, 925 etc.) or brand names or even pictures. [To this I'll add, if there are stones, have you had them tested?]
5. Measure the pearls, with a millimeter ruler if possible. If they are graduated, measure the largest and smallest pearls.
Please understand that any opinions we offer are not an official appraisal. If you think you may have valuable pearls, please see a jeweler.
Also I'll copy and paste something I posted for someone else this week, which may help you make some judgments about the pearls yourself:
See if the clasp/chain has a gold mark on it. Usually imitation strands don't have gold clasps.
Also, rub 2 of the pearls gently together or against the edge of one of your front teeth. If they feel a bit resistant or slightly gritty, that is how genuine nacre feels. If they glide very smoothly against each other or against your tooth with no resistance at all, they are likely imitation. (However coated real pearls may feel smooth and grimy imitation pearls may feel resistant.)
Imitation pearls also may have some or all of these characteristics (particularly cheaper pearls):
• extra swirls of built-up pearl-like coating near drill holes
• peeling coating that is very thin with the bead visible underneath
• beveled drill holes
• all the same size or shape, in the case of non-graduated strands (but some imitation strands have variable shapes and size pearls)
• all have the same overtones (usually none; Majorica brand have green and pink overtone colors due to the final layer of coating they receive).
• larger drill holes than real pearls have (pearls are sold by weight so drill holes are small)
• very cheap pearls with a plastic bead inside will be unusually lightweight; better imitations have glass beads and feel heavy, more like real pearls.
• glass bead imitation pearls may feel very slightly warmer against the skin than genuine pearls
• If you have a 10x loupe, look at the surface. Real nacre looks very smooth, while imitation pearl coating looks coarser textured. If in doubt compare with known-real or known-fake pearls.
Most freshwater pearls that are solid nacre are not fully round. The Chinese are now culturing smaller round freshwater pearls with beads inside that are round, but they are not yet commonly found.
