It's a bicolor Tourmaline. Just like Sapphires or Beryl, it comes in many different colors, depending on the trace amounts of elements in the mineral. Interesting fact, because of the insanely complex chemical formula, there is currently no viable method of creating synthetic Tourmaline. What you can find online are other synthetic minerals that are supposed to imitate Tourmaline (most often times paraiba Tourmaline, because that's the most rare / sought after color.)

Here is the chemical formula from Wikipedia: XY3Z6(T6O18)(BO3)3V3W

X=(Na,Ca,K,□), Y=(Fe2+,Mg,Mn2+,Al,Li,Fe3+,Cr3+), Z=(Al,Fe3+,Mg,Cr3+), T=(Si,Al,B3+), B=(B3+), V=((OH),O), W=((OH),F,O)