Saturday, September 20, 2008

What is beach sand?

To see a world in a grain of sand and heaven in a wild flower, Hold infinity in the palm of your hand and eternity in an hour. -William Blake

Beach sand is some amazing stuff, and there's all kinds of it, from the black sands of Diamond Beach, Hawaii to the ultra-white sands of northwest Florida. Sand sculptors and geologists know much more than I would, but let's just say "sand" is no simple thing. The common ingredient is silica in the form of quartz, which makes up a majority of the sand on our beaches. Then it gets interesting.

Clay, shell fragments, minerals, limestone, gypsum, and even fossilized bones can be present in beach sand as well. Our local beach sand is fairly high in clay content because of erosion of sedimentary Rio Grand Mud, which has a reddish brown color. If you've ever seen the "clay turds" on the beach after the dredge deposits some sand on the beach, you're looking at pure Rio mud. Funny, "Isla Blanca" was rather misnamed because the sand is a brownish color, not pure white, simply because of the clay content.

Then there's the Laguna Madre, which also provides a bunch of black mud of its own due to rotting sea grass, along with a vast reservoir of calcite - a form of limestone. I have many very large calcite crystals from the Port Isabel channel area, some rods about 3-4 inches long or roses of several inches in diameter.

You'll notice some very old shells on the beach too, some turning a brownish color due to leaching and mineral deposition. These dark shells are probably over 10,000 years old when the island first formed. Mineralization is most likely from iron in the form of hematite; also, fossilized bones will also assume a darker color. One academic paper blames these minerals on the Trans Mexican Volcano Belt, if you're into petrography and words like "

Yeah that was my reaction too, what-pathic?
Go see a huge Mastodon tooth at the Beachcombers Museum on Pompano Street ... easier to pronounce ... it is very dark colored.

But a case can be made that the SPI area between Mansfield Cut and the Rio Grande has a very special kind of beach sand, like none found elsewhere in the world.


Joni said...

There is so much to learn about my new home and what makes our sandbar the special place it is. Oh, and it makes me feel good to use that pronoun "our". Maybe someday I will even become a true Islander.

Love the Blake quote, too.

Lucinda said...

You're singin' my song, Sam!
It is wonderful and amazing stuff - and excuse the tawdry promo here but folks in these parts will get to see just how amazing it is starting Oct. 16, 2008 when some of the best sand sculptors in the world (including the current world champion!) converge upon Isla Blanca Park for Sandcastle Days.

Another of my favorite quotes --

"Safe upon the solid rock the ugly houses stand:
Come and see my shining palace built upon the sand!"

-Edna St. Vincent Millay

Everett said...

Off topic a little, but a friend of mine sent me a lot of pictures of the Galveston beaches and they were truly amazing
1 I've seen hurricane damage before but this one just turned those houses too kindling and swept the beaches clean! Are they going to be allowed to build right back to the waters edge again? I damn sure wouldn't. Oh well I feel for all those folks who lost everything, and if it was me, no matter how much I loved the place, I think I would hnt for higher ground.

Sam said...

That's an interesting one, Everett. The state agency that does that work has granted a 120-day suspension of the Texas Open Beaches Act to allow reconstruction of houses. Then they will fly aerials and map the "new" coastline. Anybody with a house in the water (mean high water line) has to move it because that's submerged state land.

New or rebuild houses (more than 50% damaged) would have to back up inland, called a coastal set-back. This is figured from a "vegetation line" although one has to wonder if there is any vegetation left on Bolivar Peninsula!

Wasn't that storm something? Of the thousands who stayed behind on the coast, only about 50 died, and most of those were inland (falling trees, breathing generator fumes, etc.). The reason was probably because the storm surge was only about 12-14 feet and not the 25 feet as predicted by the models.