black in sand

[arkiegirl]

I noticed this year there was more black sand. we have always been amazed at the fact that you walk across the white sand and it doesnt burn your feet and it makes that cool noise. However, this year was different and on one occasion several in our group burnt the crap out of our feet walking back to the walkway. I noticed areas where it appeared there was more black sand or something. My husband noticed when digging there was a layer of it.

Is this something that has washed in or been brought in?

 

[Matt J]

This area used to be a bog/marsh. The black sand and layer of dirt under the sand are a remnant of that.

 

[Paula]

I heard that millions of years ago the beach used to be a cypress forest and the black is "peat" from that forest. I don't know if this is true, though. I don't know why the sand would be hotter in parts, but I'll see for myself in August (can't wait, no matter if the sand is hot or cool on the feet!).

 

[Rudyjohn]

I heard that millions of years ago the beach used to be a cypress forest and the black is "peat" from that forest. I don't know if this is true, though. I don't know why the sand would be hotter in parts, but I'll see for myself in August (can't wait, no matter if the sand is hot or cool on the feet!).

this is exactly what I've always heard. But don't know how true this is.

 

[Matt J]

I heard that millions of years ago the beach used to be a cypress forest and the black is "peat" from that forest. I don't know if this is true, though. I don't know why the sand would be hotter in parts, but I'll see for myself in August (can't wait, no matter if the sand is hot or cool on the feet!).

The black sand attracts more sunlight and thus reflects more heat. Similar to why the asphalt is always hotter than the concrete sidewalk. ;-)

 

[Will B]

I had this same discussion a while back on the board with somebody who claimed to be a closet geologist. He explained what it was, but I can't find the threads. He said it was some mineral. Personally, I don't know what it is other than hot on the feet!

 

[Matt J]

Mica maybe? It's also got a little bit of a sheen to it.

 

[BeachSiO2]

I had this same discussion a while back on the board with somebody who claimed to be a closet geologist. He explained what it was, but I can't find the threads. He said it was some mineral. Personally, I don't know what it is other than hot on the feet!

Not closet geologist, but close enough. I actually get paid.

Mica maybe? It's also got a little bit of a sheen to it.

Mica's are typically much softer and lighter, and are "sheet-like" so they don't survive the beach energy that well.

It's a mineral called ilmenite. The reason you see it in layers is because it is heavier then quartz and as hard. It makes up about 2-3% of the sand on the beach. So, when storms come in and "re-work" all the sand on the beach, the lighter sand is pulled offshore (quartz) and typically a thin layer or crust forms on top of the remaining sand. Then as the quartz makes its way back on shore, it covers up that crust forming the layers. You can actually get an idea of storm history and smaller erosional and accretional events based on those layers.

As for peat, it does underly our beaches and is also dark/black. The reason is just what was posted earlier, there use to be a marsh where our beaches are now. The difference is that the peat is oily to the touch and typically requires mineral spirits to remove. In many areas the peat is only a few feet (less than 3) under the white sandy beaches. So, if you are seeing it in layers and it feels like sand, it is likely ilmenite. If it is in clumps and is oily, it is likely peat.

If you want to see the peat, go look in the dunes in Seacrest in front of Tranquility by the Sea, or the beach in the Seacrest area after a hurricane or tropical storm.

 

[Will B]

Not closet geologist, but close enough. I actually get paid.

Yup...It was you. I remember, now. Thanks for chiming in. I don't know why I couldn't find our thread...

 

[jensieblue]

Long ago I would dive the pass between St. Andrews and Shell island. toward the St. Andrews side, remnants of an ancient Pine forest were visible. I don't know wheter the trees were logged or swamped when the pass opened. , But, the dark sand was evident all around the ancient trees. Divers that liked to venture further out than me, told me that pockets of the dark sand were evident all along the beaches wherever wood decay was kept in the sand. They also told me the trunks of the ancient trees were fossalized...but then they also told me there were no sharks in the Pass and that I should eat chili before going out on the dive boats. But, gosh, I loved those days and those guys!!!!