That would be a unusual cut for a andalusite stone of that size. It almost certainly would have taken a cut that would have protected its value... square/rectangular, oval, circular (in order of commonness). Any other cut really degrades its light shifting and color changing characteristics. Its not unheard of for it to be cut in other shapes, but its not a good sign.
Easy test that helps (but doesn't guarantee), stone should change colors depending on angle of viewing, especially around the edges of the facets, should be a true color change, not a lightning or darkening of the existing hue. View from side or off angle, if it shifts to a greenish more or less shade, a real good indicator.
I tried blowing it up to see, but couldn't tell, any surface scratches or with a low magnification glass can you see any wear marks where it is set? Is it an open or closed setting on the back?
My first guess would be colored zircon or maybe even glass costume, if it shifts color... then might be worth a 100 to find out hehe.
Ram0029