Pearl Necklace from my Great-Grandma

This use to belong to my great-grandmother who was born in 1904. I know very little about vintage jewelry. As far as I know, it is costume jewelry, but if you have any suggestions and descriptions that will help in my search to find more information, it would be very much appreciated! Thank you!

This piece:
This appears to be the original box. I looked on the back of the hook itself and found "JAPAN". To my "non-collector" mind that sounds like the modern day "Made in China". Could it have meant something else years ago? Also, there is a slight possibility that this particular necklace belonged to my grandma...my grandpa was in Japan for WWII and brought back some silk and loose gems. I didn't know anything about this necklace, but I guess there is a chance he brought this back too, unless the "JAPAN" is only used on exported items...

My Story:
I use to beg my great-grandmother to open the antique steam-trunk, which was carefully nestled into a corner at the end of the hall upstairs in the house that she had lived in since before my grandma was born.

We would sit for hours while she carefully unwrapped tissue paper from treasures like her mother’s brown silk wedding dress and cream crocheted wrap that looked like airy lace. There was a clear round hatbox with a mauve quilted-satin base and lid. Sometimes she would let me wear the hats and show how ladies use to use pins to keep them from blowing away in a breeze. My favorite treasure was a dress she wore as a young woman. It was a floor length Victorian style and the perfect shade of red with long sleeves, buttons running up the back, and intricate stitch-work at the cuffs and neckline. I loved that dress, and when I turned thirteen, she wrapped it with my favorite white fur hat as a birthday gift.

Then there was her jewelry box, which she kept on her vanity in the bathroom; it shared that space with her makeup, powder puff and ornate perfume bottles. Oh how I loved gazing at all the beautiful sparkling necklaces and earrings that looked like they belonged to a princess. I don’t remember hearing any stories about the jewelry, but when the time came for them to be passed on from my grandmother, my mother thought I should have them. So here we are, with the beautiful jewelry I have treasured since I was a child, and I know very little about it! I have two little girls; the three year old has already started asking if she can wear it… and so my obsession has begun, to find out more about these, and the many other, treasures of my family history. This is only the beginning!