What type of Pearl?

I have this strand of pearls my husband gave me in the early 90s and we'd like to determine the value. We know they are real and when they are held in direct sunlight they are not the exact same size and you can see a thin line between the luster(?) and the body of the pearl. It does have a two-tier flower petal clasp that has silver stamped on the back. We purchased them in Japan; my husband thinks they are Mikimoto pearls, but not completely sure. They have no M marking.