I'm guessing (and this is just a guess) that you are talking about a piece of Tourmaline- most likely Watermelon Tourmaline.
Google Search "Watermelon Tourmaline" for similar photos or you can see if this link https://crystal-cure.com/facet-tourmaline-watermelon.html looks similar to your stone.
The colors of Watermelon Tourmaline are generally..."a rare variety of tourmaline that displays three different colors in the same crystal - green (the skin of the watermelon), pink (the sweet fruit) and white (the rind)." (see Crystal Cure Link).
Here's more photos of Watermelon Tourmaline : http://www.mineralminers.com/html/tmcgems.stm
Hope this helps!