Principally, gemstones are found in the alluvion gravel deposits where ancient rivers used to run or the rivers and their banks in present day gorges and paths.
For example, in Ceylon, the rivers carry rubies and sapphires far from the original sites and deposits. By sifting and sorting the gravel beds all along the river beds and banks, then washing away the extraneous rock and gravel, miners find a few rubies and sapphire crystals a week.
The process of searching for alluvial gem deposits (river carried gems) goes back into prehistory—tens of thousands of years ago.
Panning for gold, gems, and diamonds in this manner is as old as mankind. One can spend a life time looking for the really large or significant find. Frequently, the key to finding gold or gemstones is to search where the ancient rivers used to flow—millions of years in the past. Many present hunters find gold and gem rough in sedentary rock.
Once a person has made a find of gem crystals, he sells them to another person who buys the crystals from all the miners working the rivers in the area. This buyer, when he has collected enough crystals to make it worth while, takes them to the large cutting centers.
An expert planner at the gem cutting company then looks at each crystal over a high intensity light table. Most gems are graded wet, or with a side polished, so they may see inside the stone. The rough gems are then graded to size, color, and clarity. These rough gems before grading are called mine run.
After the sorting and grading takes place, a price is agreed upon and a deal is struck. Only 20% of the mine run gems are cuttable. However, it is the custom to purchase all the rough the miner or purchaser has brought in. Many times the cutter or purchasers can’t agree on a price they feel will allow them to make money and the seller will reach into his pocket and pull out some really large quality rough gems to make the deal happen.
Years ago, I used to go to the Indian Reservations in Arizona and buy mine run peridot and pyrope garnet (ruby colored garnet), because the ants loved the pyrope garnet and made their large ant hills out of as much of it as they could find. I always wondered what magical qualities the ants found in this beautiful gem. The Indian name for pyrope garnet is ant hill garnet.
Peridot was formed in the caldron of volcanoes, as were diamonds. The dry river beds of Arizona contained both of these gemstones and the Indians who sifted the ant nests and river beds earned substantial amounts of money. They would never take you to their mines and even guarded their location from each other.After the sorting, we shipped the kilos of rough to Sri Lanka and had it diamond cut and shipped back.
Every February, we would take a large portion of the cut gemstones to the Tucson gem and mineral show where we would wholesale it to jewelry manufacturers and gem dealers. The first hand experiences and the hundreds of hours of inspecting rough gems gave me a real appreciation of gems and what it requires to end up with a quality gem stone or diamond.