sand - olivine and coral - set of five tubes of olivine sand weathered from basalt with coral sand derived from a reef

Sand is derived from whatever material is locally available.  Beaches are uncommon on the seacliff-ringed Island of Hawaii.  Occasional small coves have sand derived primarily from basalt unless there is a coral reef offshore. This sand was collected in 1994 from a tiny cove near South Point, Hawaii, where a local concentration of olivine had weathered out of the basalt and was concentrated by the waves. An offshore coral reef contributed about half of the grains in this sand. Olivine forms at temperatures and pressures found in the earth's mantle and is carried up from a mantle hot spot in the basalt that forms the Hawaiian Islands. It is almost twice as dense as quartz, which is the typical source material of the white sand beaches of the continental USA, so it is not as easily swept out to sea by wave action. Because of the offshore reef, some grains of this sand are composed of coral or shell material.  Hawaii's white sand beaches at Waikiki were initially an import, from Californi