Rubies found at Sivec Mountain, have been mined for thousands of years. It is a marble mine in the Republic of Macedonia. These aren't on the market regularly, and when they are good with a dramatic color contrast from red to white, they are excellent examples of rubies in matrix. 

This Ruby is a big floater that formed in marble. It's about the size of a large walnut. It is well crystallized and has great color, especially for its size. The second pic is under long wave fluorescent lighting. On the backside there is a spot where the color changed into blue/purple sapphire. It's in great condition, no dings. There may be a cleavage plane on a subcrystal face on the right side (pictured), it fits in with the overall form and may have happened during formation.