![]() Most of them are under 2 millimeters in diameter, but a very few are more than 2 millimeters across, which puts them above "sand" and in "gravel" territory. ![]() Here's a recent image from MAHLI that clearly contains quite a few fairly coarse grains. I'd love to see more examples.)Īnyway, back to Mars. I am sure there are more very silly or funny ternary diagrams among some geo prof's slides somewhere. (Aside: I looked really hard yesterday to find funny ternary diagrams, and that's the best one I could find, thanks to a tip from Patrick " Poikiloblastic" Donohue. If you're not quite sure you get how a ternary diagram works, here's an amusing exploration of the phase equilibria of pie crust that employs a ternary diagram. A pure sand would plot at the "sand" corner, but if there's some clay in your sand but not very much silt, it would plot in the "clayey sand" region. In a ternary diagram, three endmembers are represented at the corners of a triangle, and you represent the proportion of those three endmembers in something by plotting a point somewhere inside the triangle. So you can have gypsum sand like at White Sands National Monument, or olivine sand on certain Hawaiian beaches, or any other composition where mechanical and chemical weathering bust rock of any composition into sand-sized particles.īoth the Shepard and Folk classification systems involve a graphical tool beloved by geologists: a ternary diagram. But the term "sand" does not specify composition, it only specifies grain size. When we think about sand, we usually picture quartz sand, because that's what most sand is made of on Earth. Gravel is anything larger than that silt and mud are finer. Wentworth defined "sand" in a publication in 1922, along with "gravel," "silt," and "mud." Sand-sized particles range in size from 63 microns to 2 millimeters. Just as with "rock," for geologists, "sand" has a definition that is far more precise than the way that the word is commonly used in conversation. How can the word "sand" possibly be confusing? Well, the situation is a lot like the one with the word "rock," which I talked about in this blog entry. I had one of those "A-ha" moments last week where I suddenly realized that I had run afoul of a common problem in science communication: when the words I'm using mean something different to me than they do to almost everyone I'm talking to.
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