These are man-made, or synthetic, sunstone pendants, not to be confused with the real mccoy Sunstone that we also have in abundance. They look somewhat like synthetic goldstone, only this is considered an even nicer stone and I tend to agree. Very sparkly and very good value if you need an eye catching focal piece that is big and doesn't cost the earth.
The vast majority of these pendants are between 30mm and 40mm with many in the 35-40mm range. Oval, square, drop, rectangle, and triangle. Lots to choose from!