Gem quality coral is related to reef forming coral but the most valuable coral variety is found in the mediterranean the red sea and in coastal japan. Coral is an ancient gemstone and has been used for thousands of years. Make offer 100 natural red coral aaa quality gemstone polish rough 34 x 42 x 16mm 21 25cts 100 natural red coral fine quality gemstone polish rough 20 x 46 x 06mm 12 30ct 49 99.