Happy 4th of July everyone! As we gear up to celebrate Independence Day with fireworks and barbecues in the sweltering heat, we wanted to figure out a fun way to mark the occasion.
This is the first of a series of blogs examining the “science of summer” as we explore the underlying science behind summer-based themes. We’ll be answering deep questions like how does sunscreen work, what are the economics of a lemonade stand, and for today, why beaches have different colored sand.
It turns out that, well, it isn’t really rocket science (like my normal job), but more a matter of geology! The sand, as you would guess, is really just tiny bits of rock that have eroded from the local geology. So the color is pretty much determined by the mineral content of the local sediment and rock. In honor of the 4th of July, I figured we’d look at red, white and yes, blue sand!
Let’s begin with red sand. Red sand is pretty easy to understand. It’s found in areas which are rich in iron (iron-oxide, commonly known as rust, is red-colored). Kaihalulu Beach in Maui is a famous example with the iron coming from the continual erosion of the volcanic cinder cone located behind the beach. Prince Edward Island in Canada is also a pretty unique place as the entire island is composed of iron-rich red- sandstone sediment resulting in very deep-red soil and red sand beaches!
As for the white sand. Well, I am sure everyone is picturing a beautiful tropical paradise with turquoise water and long stretches of white beach. It turns out that white sand is composed of finely ground quartz crystals. Crescent Beach on Siesta Key in Sarasota, FL won the 1987 Great International White Sand Beach Challenge for the whitest sand in the world. The quartz actually originates from the igneous rock in the Appalachian mountains and the eroded material is carried into the Gulf by the major rivers.
And finally, blue sand! This is, by far, the coolest type of sand and can be found on Redang Island off the coast of Malaysia. Unlike the other sands, which are dominated by geological processes, blue-sand is biologically-inspired. It turns out that tiny creatures from the class of ostracods (related to crustaceans, like crabs, lobsters, etc.) can be bioluminescent, giving off a blue-glow. Try imagining the marine equivalent of fireflies. These little guys are tiny (less than 1 mm in size) and are mixed in with the sand. As night approaches, they light up making it seem like the sand is glowing a nice blue color.
I hope you learned a bit about our world’s patriotic sand! If you’d like to see more colorful beaches, check out this site showcasing the world’s most unusual colored sand! Stay-tuned for more on our summer series. If you’ve got a burning summer science question, please post a comment below and I’ll try our my best to answer! I hope you have a great fourth of July and if you are on the beach, be sure to teach your family and friends a thing or two… or three about sand!