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March 15, 2008

Sorted Sand

Filed under: Sand, Sea & Sky by Bill @ 11:00 am

We had some pretty rough weather last weekend and while visiting the beach I saw some striking bands of red and black sand tossed up by the waves.

waves at the beach
Whitecaps and waves on the Great South Bay

This is a common sight and you’ve probably noticed these colors in long strips running lengthwise down the beach. The colored sand is composed of garnet and magnetite in roughly a 52/45% proportion with the remaining 3% composed of other minerals. The soft white sand that makes up the majority of Long Island’s beaches is quartz.

bands of garnet and magnetite
A lot of garnet and magnetite on a beach at the East Islip marina

As a kid I always wondered why and how the red and black sand grains gathered together. It wasn’t until my junior high school science teacher, Mr. Lewis explained it to me that the mystery was solved. The garnet and magnetite are much denser than the quartz, so wind and wave action affect those grains differently. That tends to sort them out from everything else.

If you want to look like a geek next time you go to the beach, bring a magnet and magnifying glass (like I do). Drag the magnet through the sand and then look at it with the magnifying glass. You’ll see that it picks up black grains of the aptly named magnetite, which is composed mostly of iron.


  1. Bill,
    Great bit of Long Island TRIVIA….and information, as well….

    Love all the pix……love the BLOG…..GREAT STUFF!

    Comment by Debra Ann Kasimakis — March 17, 2008 @ 3:17 pm

  2. Hi Deb,

    Nice to hear from you. Thanks for the compliments…I try. -Bill

    Comment by Bill — March 18, 2008 @ 7:25 am

  3. Hi Bill,
    Love the idea of collecting, fossicking etc. To do it on a beach would be so much fun. Do you actually get large specimens? Have you dug down deeper to search?

    Comment by Marylyn — April 11, 2008 @ 7:35 am

  4. I love to dig on the beach. I don’t really find much, just small shells, old bottle caps, and the occasional diamond ring 🙂

    But it is interesting and I love the small world revealed by the magnifying glass. Sometimes I find baby clam shells as small as a pin head. Sometimes I’ll dig deep, but most of the time I’ll just dig as far as a palm sized clam shell will take me.

    Comment by Bill — April 12, 2008 @ 8:39 am

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