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A Rambling Writer Guest Post: Geologist Thor Talks Marble

Join my paleontologist/geologist husband Thor Hansen as he talks about our fascination with marble pebbles we collect on Greek beaches.

Today we talk about marble.  Marble is beautiful, relatively easy to carve, and takes a nice shine, so it is no wonder marble is prized for sculpture and the interiors of buildings (not so good for outdoor projects because it dissolves in acid rain).  Marble is metamorphosed limestone, i.e. limestone that has been buried and heated and squeezed by geological processes.  Most of the rocks you see every day are silicates, meaning they are composed of silicon, oxygen, and probably several other elements like iron, magnesium, and aluminum.  Silicates comprise the vast majority of rocks on Earth and are formed deep underground under high temperatures and pressures.  Limestone, on the other hand, is organic.  Marine organisms like corals, clams, snails, and algae extract calcium carbonate from tropical sea water to make their shells/skeletons.  A coral reef system typically has a strong coral/algal reef that protects a quiet water lagoon.  On the reef and in the lagoon the busy little carbonate secretors make their shells, which turn into lime mud after they die.

In the image below Sara is snorkeling around a patch reef near Xcalak, Mexico.  On the right you can see corals, sponges, sea fans, and coralline algae.  The white stuff on the seafloor is lime mud formed by the degraded reef organisms.

When you go to a place like the Yucatan Peninsula (think Cancun, Tulum, Playa Del Carmen), everything you see or walk on was created by reef organisms.  Below is the beach at Playa Sonrisa near Xcalak.

I’m posting my complete blog entries on my own author website at, where you can finish this episode and enjoy all the accompanying photos. Please continue reading by clicking on the link below, then you can return here (use “go back” arrow above) to comment, ask questions, or join a conversation. We love your responses!


You will find The Rambling Writer’s blog posts here every Saturday. Sara’s Greek islands novel  from Book View Café is available in print and ebook: The Ariadne Connection. “Technology triggers a deadly new plague. Can a healer find the cure?”  The novel has received the Chanticleer Global Thriller Grand Prize and the Cygnus Award for Speculative Fiction. Sara is at work on the sequel, The Ariadne Disconnect. Sign up for her quarterly email newsletter at



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