Gemstones Concentrated by Surface Waters: The Gem Gravels of Sri Lanka

  • Peter C. Keller


When gemstones are hard and tough enough to withstand mechanical breakdown, chemically resistant to attack by natural acids or bases, and dense enough to be concentrated, they can form secondary placer or alluvial deposits. Diamonds, rubies, sapphires, jades, tourmalines, topazes, spinels, aquamarines, and chrysoberyls are but a few of the minerals that may be freed from the softer parent rock by weathering, eroded and transported down a slope to the nearest stream, and further carried along by river currents and/or wave action. Moving stream water sweeps away the lighter minerals, and the heavier placer minerals, such as diamond and corundum, sink to the bottom or are moved downstream a relatively short distance. Waves and shore currents also separate heavy minerals from lighter ones and coarse grains from finer ones. From thousands of tons of debris, the few heavy mineral grains in each ton of rock are gradually concentrated in the stream or beach gravels until they accumulate in sufficient abundance to be worth mining.


Source Rock Heavy Mineral Parent Rock Placer Deposit Diamond Deposit 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Van Nostrand Reinhold 1990

Authors and Affiliations

  • Peter C. Keller
    • 1
  1. 1.Natural History Museum of Los Angeles CountyUSA

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