Congratulations!! You have discovered a Tanzanite!
Tanzanite is the blue/purple variety of the mineral zoisite discovered in the Mererani Hills of Tanzania in 1967. Tiffany & Co. named the gemstone after the country is was discovered. It is known for its trichroism - appearing alternately blue, violet, and burgundy. Tanzanite is a rare gem - only found in the foothills of Mount Kilimanjaro.
Since tanzanite is relatively soft, it is typically set in necklaces and earrings.