Close of up sand

What is Sand Made Of?

We love playing at the beach and enjoying the ocean, and we also love learning about it. It turns out that there’s a lot more to know about the Science of Sand than we ever would have guessed!

To help us better understand the science of making sand castles, and to get smarter about healthy beaches and healthy oceans we have our very own literal "Professor of Sand”!  Art Trembanis is a Professor of Oceanography at the University of Delaware, and is our go-to expert on all things sand, beach, and ocean. We invited him to start with the basics and tell us what sand really is!

Pufferfish: So, Prof. Art, first and foremost, what exactly is sand?

Prof. Art: Sand is primarily made of broken down fragments of rocks that have been weathered over an incredibly long time and transported to the beaches after a long journey from their original source high in the mountains.  In the case of some coral beaches sand can come from parrotfish poop!  


That’s right!  Parrotfish (and other herbivorous fish) bite away fragments of coral and then poop out sand. The white sandy beaches of Hawaii for instance includes lots of sand made from parrotfish poop. Other beaches in Hawaii are famous for their green sands that are derived from a volcanic mineral called “olivine”.

So what makes it sand, not rock?  

The size!  As soon as it gets small enough, it’s considered sand. Sand can be made of almost anything as long as it’s small enough. 

How small? 

Well, sand is finer than gravel and coarser than silt.  Does that help? 


Scientists and engineers have established precise and standardized definitions for particles of different sizes and the agreed upon definition for sand is particles between 0.0625 millimeters  to 2 millimeters.  Even within the sand sizes there are further subdivisions from largest (very coarse), to coarse, to medium, to fine and finally to smallest (very fine) each with a defined interval.  

Why make such a big deal about such a small thing (or small things)?  

Because knowing the grain size is fundamental to understanding how the sand will behave and that’s the basis for building a great sand castle!    

Thanks, Prof. Art!


Have other questions you'd like Professor Art to answer? Leave them in the comments below!

Want to know more about what sand is made of? This website for arenophiles (people who love sand) is a great place to start! Additionally here are 20 interesting facts about sand to help you amaze and astound your family and friends.

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