Answer: Ruby gemstones occur in Tanzania as well as in neighboring Kenya. However, if you find “Serengeti rubies” offered for sale, be aware that they may not be from the famous Serengeti region. They also may not be rubies at all.
Cape Rubies, River Rubies, and Serengeti Rubies: Beware of Gems With Two Names
Based on your description of their color, these so-called Serengeti rubies may not be rubies. In the strictest gemological terms (and to the unaided eye), ruby is gem-quality red corundum. Only a competent professional gemologist can identify and appraise your rubies.
Many gems have been given two names to mislead the buyer. There are a few with the second name of “ruby.” The most famous example of this was the “Cape Ruby.” In the 1930s, many people paid a high price for rubies but found to their dismay they had bought pyrope garnets. In the 1950s, “River Rubies,” said to be from the Congo River, turned out to be garnets, too.
Buyer beware. Do your homework before you buy that gem with more than one name!
Ron Campbell, Central Coast Gem Lab
Basic Information About the Value of Rubies and Sapphires
Vendors sell many stones with exotic or colorful modifiers attached to the names of well-known and valuable gems like diamonds and rubies. Unfortunately, these stones are often another less valuable gem species. From your description, your Serengeti rubies might be garnets.
Assuming your Serengeti rubies are actually corundum, they would be valued as either rubies or sapphires, depending on their color. Many gemologists don’t consider pink corundum stones rubies.
As far as where the stones are from, I don’t know of any ruby or sapphire which has a price premium attached to it solely on the basis of locale, except for Kashmir sapphires or Burmese rubies of known provenance. So, assuming your Serengeti rubies are really rubies, no matter where they’re from, they would be graded based primarily on size, clarity, and color. Since rubies are usually included to some degree, color is the most important factor, assuming the inclusions aren’t preventing transparency. The cut would be a secondary consideration.