What causes color differences in beach sand?
ilovejules25 asked:
Most beach sand is some shade of a tan color, some more white than others. But in certain areas the sand is a very dark shade of purple… why is this? I’ve read that in places like Hawaii, sand can be pink because of the effect that lava has on it. But where I’m from (Long Island, NY) there sometimes can be seen large patches of dark purple sand on the beach… and there’s no volcanic activity there. So where does that purple sand come from?
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Most beach sand is some shade of a tan color, some more white than others. But in certain areas the sand is a very dark shade of purple… why is this? I’ve read that in places like Hawaii, sand can be pink because of the effect that lava has on it. But where I’m from (Long Island, NY) there sometimes can be seen large patches of dark purple sand on the beach… and there’s no volcanic activity there. So where does that purple sand come from?
May 31st, 2010 at 7:43 am
The color has to do with the color of seashell that are find there and the color of coral.
June 1st, 2010 at 9:21 pm
well, the color of the sand at any given beach depends on the rocks/ minerals the sand is made up of. In Hawaii, the volcanic beaches are made up of BLACK sand (not pink). also in Hawaii, there is a green sand beach made up of the rock olivine. a pink sand beach can be found in the Caribbean, and its made up of coral. Pink sand has nothing to do with volcanic activity. as for the dark sand you see on Long Island, its most likely dirt mixed with the sand. I also live on LI, but never go to the beach here just for that reason, the beaches are filthy.
June 5th, 2010 at 6:42 am
depends where the sand come from…its usually from a nearby mountains… for example in california the mountains are made of granite so the beach sand tends to be quite gray the caribean has several limestone mountains so it tends to be powdery sand and an Island in Hawaii the sand is black because of the volcanic minerals I think that that sand come moslty from Basalt.
June 6th, 2010 at 6:11 am
To a geologist (me) their is no such thing as sand. Sand is actually a grain size. What you see on the beach as sand is actually uniform tiny tiny rocks composed of the surrounding area or even from distance places to.
As far as New York not having volcanoes is not actually correct. Major orogeny (building) of events in the past have developed volcanic deposits both above and underground.
The sand you seeing today could be the remains of such activity long ago.
As far as the color differences all depend on the “rock” the “sand” is made of. It could be a Si based structure to metamorphic and everything in between.
Also due to overshore currents (which make barrier islands) the sand your standing on in Long Island could be from hundreds of miles away up north.
Anyway, that is the idea, basically.
June 7th, 2010 at 5:10 am
The colors of beaches are directly related to the sources of the sand. The darker sands contain more dark minerals, the very light, white sands are typically macerated calcareous material from reefs or shells.
The purple you have seen may well be manganepidote or piedmontite, often associated with glaucophane-bearing rocks in the crystalline-schist. These shists can be found in the mountains to the northwest of Long Island. The rock which contains piedmontite as an essential component is well characterized in outward appearance, being of a dark violet colour.
In your case on Long Island, the island itself is a remnant of a glacial terminal moraine which has moved rock and sediments from the northwest to Long Island Sound. So, the various minerals transported by the glacial activity can leave a variety of colors of sands from the varielty of rocks the glaciers abraded on the way to Long Island Sound.