Brooch or sash pin with a large faceted blue glass "stone". This style was popular from about 1890 - 1900,
The brooch measures 1 3/4" x 1", with a narrow brass setting and c-clasp. The glass is light blue, and faceted, and was probably meant to be worn against a white background. The British rule of India yielded many spectacular gemstones for the ultra rich. Large stones, such as amethyst or blue topaz, worn by the very wealthy, were imitated by the simply "well to do".
The glass shows minor scratches under magnification. The brass setting has darkened. The c-clasp is in good working order.