I was thinking about this struggle to build on sand, and wondering why all grains of sand are similar in size. As rock breaks down, eventually it's so small that it gets carried by the wind and I wondered if at some size it encounters less friction with its neighbors that it doesn't break down as fast into smaller particles and forms endlessly roving sand dunes. I wasn't able to find a specific answer, but found some interesting discussions.
Guess what Hawaii beaches are made from?
"The famous white-sand beaches of Hawaii, for example, actually come from the poop of parrotfish. The fish bite and scrape algae off of rocks and dead corals with their parrot-like beaks, grind up the inedible calcium-carbonate reef material (made mostly of coral skeletons) in their guts, and then excrete it as sand."
Sand from land erosion on beaches is in transition from large river rocks to dissolved sediment that gets carried out into the ocean and settles on the ocean floor.
"sand grains on our beaches are not at the end of their life: these tiny rocks have likely been sand before, and will be sand again. Sand grains get deposited in layers on the ocean floor, and once they are buried deep enough, the pressure transforms sand to sandstone...sand creation is a continuous process that is part of a larger rock cycle"
The processes of sand formation are well described on this page:
"Geologists describe sand by measuring the roundness of grains and the distribution of grain sizes... Roundedness usually gives information about the length of transport route and distribution of grain sizes helps to determine from which environment these grains come from. River sand is usually poorly sorted and compositionally immature. Beach sand is more rounded and eolian [created by the wind] dune sand is generally well sorted...The average size of grains is determined by the energy of the transport medium. Higher current velocity (either stream flow or sea waves) can carry heavier load. Coarse-grained sediments therefore reveal that they were influenced by energetic medium because finer material is carried away...sand occurs in a harsh environment where only the strongest survive. By "strongest" I mean the most resistant to the weathering processes. Quartz is one of these minerals but not the only one. It is so dominant in most sand samples because it is so abundant. 12% of the crust is composed of ....quartz is very resistant to chemical weathering. It does not alter to any other mineral — quartz is quartz and will remain that way. It eventually goes into solutions but VERY slowly. Hence, disintegrated granite yields lots of quartz grains which will be transported mostly by running water as sand grains. " [see illustrations at:]
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