I looked at the photos, but just so you know, if you are uploading photos from a smartphone you need to use the desktop version of Pearl Guide, not the mobile version. There is a little icon of a tiny photo of a tree-- it's the 3rd icon to the right of the smiley. Click that and upload.
As to the pearls, they could be freshwaters. The way they are finished is low end. Very unlikely they are south sea pearls.
They could also be imitation. Imitation pearls are commonly knotted. They are so grimy that it's hard to see any luster, and it could be grime that is making them feel gritty or sticky when rubbed together. Also, it's hard to see luster against a dark background. Pearls are best evaluated against a white background.
Do this: Wash them with a warm solution of soap and water, and test for grittiness again. If they glide smoothly, they are imitation. If they still feel gritty, place them against a white background (paper towel is fine) and photograph them again. Provide close ups of any blemishes.
Also check the clasp again for any other markings.
