The two bangles with rhinestones are celluloid. These are unusual in that the most common type of celluloid jewelry I see are celluloid bangle bracelets and pins in a pale cream or white color, with molded flowers painted in a pastel color. Celluloid was used to make pins, hat pins, bracelets, beads, etc. Today it is still used to make guitar picks.
The dress clip shown below is more typical of the type of celluloid flower jewelry you might run across in the marketplace.
Celluloid is many times quite lightweight and the creamy colors remind me of chalk. It did come in black, which I haven’t often seen. I have a red bangle which has been coated in red, then carved so that the creamy white color underneath is exposed.
To test for celluloid, do NOT perform any type of pin test. My advice is to google lots of photos of vintage celluloid and get a feel for the common styles of celluloid jewelry. Pinterest has some excellent examples of the common styles of celluloid jewelry as well as some fantastic colors and designs in less common pieces.
I am happy to look at photos of your jewelry if you need some direction. Email me at firstname.lastname@example.org.