The sand on beaches in different parts of an island may be
differently-colored because of the undersea coral reefs nearby and the
ocean currents that affect the locations involved by carrying
different types of minerals and sea creatures to the area. White
beaches are usually made of coral and/or of transparent quartz (washed
from nearby land masses). A beach which has a frail coral reef nearby
may have very fine, sugar-like white sand, while a beach with pinkish
sand gets its color from red algae, and such a beach is more likely to
be near a more stable coral reef (red algae is known as "reef cement,"
as it helps to protect the coral reef from destruction.) There are
more white beaches than pink ones because the protective quality of
the red algae tends to keep portions of a reef from being washed away,
while a coral reef without red algae is more likely to send fragments
landward. Brown sand is usually quartz with impurities such as
olivine, and often has a nearby rocky land mass as its source. Black
sand is finely-pulverized volcanic rock. Red or orange sand has a high
iron content, and oxidation similar to rust gives it a ruddy color.
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Here is an interesting breakdown of colored sands and their
components. This is specifically describing beaches in the Galapagos
Islands, but the information is appropriate also for the Caribbean:
"White Sand Beach...
white corals, conch shells, diatoms
Brown Sand Beach...
obsidian, olivine, quartz, magnesium, magnitite
Black Sand Beach...
lava ash (in layers), conch shells, snail shells
Green Sand Beach...
olivine and quartz crystals"
Washington College: Summer Experience in Ecuador
http://www.ecuador.washcoll.edu/Syllabus-Projects/Mitch.html
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Below you will find excerpts from several sites
discussing the factors that influence sand colors:
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"Red ocean sand contains high iron content which oxidizes to iron
oxide, which is red. Black lava sand is black due to the presence of
manganese compounds, which are black. White coral/ocean sand comes
from coral, seashells, calcarious algae, which produce structures made
of calcium carbonate, a white compound. Desert (quartz) sand is
colorless or pastel transparent/translucent solid, which appears white
as its surface is abraded."
University of Hawaii: Sands
http://www.spacegrant.hawaii.edu/ScienceDemos/sands.html
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"...Beaches are predominantly white because the sand grains come
mostly from the coral reefs that surround our islands. A coral is made
up of thousands of tiny coral polyp animals that live together in a
colony supported by a hard, chalk-like skeleton. Many corals living
together form a coral reef. During high seas, storms and hurricanes,
coral reefs can take a battering as waves crash down upon them. Large
pieces of coral are broken off and carried great distances leaving
small pieces along the way. During many years of rolling along the
ocean floor, the large pieces of broken coral will release small white
grains of sand that become free to embark upon their own journey, tiny
travellers in a vast sea of blue.
But what of those pink grains of sand? Theirs is a brave story about
building and protecting the coral reef. These grains are made of the
same material as the white grains, but they are pink because of red
algae, commonly called reef cement, which has grown on the coral reef.
Reef cement is a very important reef building element that protects
the coral reef from destructive waves and storm surges. The fact that
there are not as many pink grains as there are white grains is a
testament to how well the reef cement does its job.
But crashing waves and storms are only part of the story about our
white and pink sand grains. Some arrive on the beach via a much more
interesting route! Next time you go snorkelling, take the time to
listen to the sounds of the coral reef. That scraping noise is the
sound of parrotfish feeding on the coral. The ultimate goal of the
parrotfish is to get to the algae that live in the coral animal. To do
this, the parrotfish must scrape away at the live coral with its
parrot-like beak and swallow pieces of the hard coral skeleton. As the
hard coral passes through the parrotfish it is crushed into small
pieces which eventually pass through the parrotfish as small grains of
sand, some white and some pink.
Now those black sand grains are another story . . . sometimes you see
a lot of them and sometimes only a few. Chances are there is an
exposed rocky shoreline somewhere nearby, or on a small island a short
distance away. Imagine the constant crashing of waves along that
shoreline and it becomes obvious that over time small pieces of the
black rock found there will eventually fall to the sea. The waves on
the rocks act just like sandpaper on wood, releasing small grains of
sand and leaving behind a smooth shoreline. Some grains will not even
have the time to settle on the bottom before the ocean currents carry
them out into the deep ocean or up onto a nearby beach.
The occasional orange grain that brightens up your handful of sand
tells the tale of life and death on the coral reef. Many shelled
animals with varying shades of orange, brown, purple and yellow can be
found in our waters."
BVI Welcome Online: Seeing the Beach... for the Grains of Sand
http://www.bviwelcome.com/articles/sand/
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"The Caribbean has some of the most beautiful beaches in the world. My
personal favourites are the pink sand shores of Barbuda; Vieux Fort
and Anse de la Feuillère in Marie Galante; Dark Wood Beach in Antigua;
the east coast at Bathsheba in Barbados; Coal Bay in St. Vincent and
Friendship Bay in Bequia. The volcanic islands (in particular
Martinique, St. Vincent and Dominica) tend to have black sand beaches,
which heat up more than white sand. In Martinique the beaches in the
south have white sand and those in the north black volcanic sand, but
these have the advantage of being less popular and the water is
superb. At Le Prêcheur where Louis XIV’s long-term mistress and
eventual wife, Madame de Maintenon, lived for seven years as a child,
there is a wonderful remote beach called Anse Couleuvre, accessible
only on foot but deserted, with fine black sand and huge round
boulders."
Travel Intelligence: A Caribbean Primer
http://www.travelintelligence.net/wsd/articles/art_2251.html
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"What is it that makes the sand so white? The sand isn't bleached by
the Sun. It's white primarily because of the type of rock that it
comes from, relatively clear quartz. Sand is particles of weathered
quartz... When the quartz is more transparent, photons of sunlight are
not as readily absorbed as they are by quartz grains having more
impurities, thus the quartz sand having fewer impurities appear
brighter. An object looks bright if most of the incident photons
(those falling upon the object) re-emerge. Most beaches are brownish
or tan in color since the sand that has formed them comes from quartz
having varying amounts of impurities."
Goddard Space Flight Center: With "Spring Break" Arriving...
http://www.gsfc.nasa.gov/gsfc/educ/science/1998/03-23-98.htm
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More on sand and its colors:
Wayne's Word: Sand Grains: Chips Off The Old Rock
http://waynesword.palomar.edu/ww0704b.htm
University of Hawaii School of Ocean & Earth Science & Technology:
Beach Sand
http://www.soest.hawaii.edu/GG/ASK/beach_sand.html
Microscope-Microscope.org: Sand Analysis
http://www.microscope-microscope.org/applications/sand/microscopic-sand.htm
University of Minnesota: Microscopy Image Gallery
http://www.charfac.umn.edu/MMS/ProjectMicro/Explorations/Feb1999.html
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Search terms used:
beach sand
sand colors
caribbean
island
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Thanks for asking an interesting question. I hope this information is
helpful. If anything is unclear or incomplete, or if any of the links
do not function, please request clarification before rating my answer;
I'll be glad to offer further assistance.
Best wishes,
pinkfreud (contains no red algae) |
