Tag Archives: rocks

Writing prompt: Old rock day

(It’s the new year and I going to restart my weekly prompts! Hooray! I slacked a bit this fall, which means I’m chock full of inspiration, right?)

Time: 10 minutes plus a 5 minute edit. Click here to go to my list of prompts.

“Old rock day” (Inspired by this list of silly holidays.)

After I went to an exhibit on Mars rocks, I was determined to find my own chunk of Mars. I dropped $1500 on a Pocket Geology GC™ Field Testing Kit. The Pocket GC could vaporize a small chunk of rock and run it through a tiny analyzer. Based upon the composition and structure, it could access an online database and tell you how the rock formed, where it was from, and how old it was. Crowd sourcing meant better data every day. If you really needed to be sure, you could send it off for authentic geological testing by certified scientists… for a price.

Only a handful of Mars rocks have ever been found because most rocks just look like rocks. Peering into their history isn’t something human eyes were made for. But since the Pocket GC hit market, the number of samples had grown by 50%.

I drove throughout the southwest. I studied the circumstances of other rock finds. I kept looking. I kept failing, but I was keeping busy, which is important, right?

I found it, appropriately enough, in City of Rocks State Park in New Mexico. It wasn’t a Mars rock; it was something else. I only went there for the scenery; the rocks there are way too young to find a Mars rock. But, so accustomed to fiddling with my hands, I tested an unassuming chunk of rock.

“Origins: Unknown, age: unknown,” my phone displayed, followed by a mess of chemical data. The Pocket GC didn’t return “unknown” too often these days. Sometimes scientists in the lab with new substances stumped it, but after 5 years of crowd supplied data, it had seen almost everything. So I had found something wonderful: a puzzle. I knew I should send it in for the extra testing. But I decided to keep it intact for a few days as a trophy. It was almost a compulsion, I couldn’t stand to hurt it more than I already had for the testing.

I set the rock on the bedside table as I went to bed that night. In the morning, I woke tired. The dreams crept up on me slowly over the next few nights.

Fun Science: Crystals Everywhere!

I went on a trip to DC last fall. Almost accidentally I ended up in the Natural History Smithsonian Museum. Wow! Especially worthy is the section on minerals. I assume there are other museums with such displays, but I hadn’t been to one. The Hope diamond is displayed also in the minerals section, but fancy jewels I can’t touch are way less interesting than all the minerals and natural crystals.

I find crystals fascinating because they tell you so much about the microscopic structure of the material. Where else in life can you just look at an object and see what it does down to the nanometer? So naturally the camera came out. Below are a few favorites, and some comments about what we can infer from the pictures.

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Fluorite (CaF2): As you can see, Fluorite has a cubic crystalline structure. Fluorite can come in basically any color. Color can be due to impurities, exposure to radiation, or defects in the crystalline structure. Fluorite was originally so named due to fluorescent properties; fluorite can fluoresce in a variety of colors depending upon the impurities present.

IMG_2139Beryl (Be3Al2(SiO3)6): You might be more familiar with other names for Beryl, such as aquamarine or emerald or morganite. Beryl is naturally clear, but takes on color in the presence of impurities. Emerald, for example, has chromium or vanadium present. Aquamarine coloration results when the Fe2+ oxidation state is present. Fe3+ results in yellow coloration. You can see in the image above that beryl has a hexagonal crystal structure. You can also see that this is one big hexagonal crystal, unlike the population of cubes in the fluorite picture. This tells us a lot about how the crystal grew. If the crystal grew very fast, there would be a number of columns, because crystallization would be faster than the time for the mineral components to diffuse to one specific column. So this crystal grew pretty slowly.

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Wulfenite (PbMoO4): Wulfenite is often found around lead deposits, which makes sense since it contains lead. It has a tetragonal crystal structure, and tends to be yellow or orange or brown in color. You can see that the crystals are much smaller in this picture than the beryl crystal. Clearly these crystals grew quickly from many nucleation sites. The size to which crystals tend to grow is a property of the crystal too; some only form a ton of small crystals, some form a few very large ones. It depends whether it is lower energy to just form another crystal, or if it is lower energy to allow diffusion to an already established crystal. This is related to thermodynamics. Wulfenite seems to favor lots of small crystals. Some wulfenite has a really cool property called piezoelectricity; when there is the right kind of pressure on the crystal, an electric charge accumulates.

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Manganese dioxide (MnO2): This manganese dioxide has grown in a dendritic fashion. It might look like frost or snowflakes, which grow in similar ways. These dendrites are very fractal, a favorite topic of mine. Here diffusion was definitely limited, so crystals grew where the materials were present.

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Chalcedony (SiO2): Chalcedony is a type of silicon dioxide, which is the chemical composition of most sand. Chalcedony is composed of two different silicon dioxide minerals: quartz and moganite. Quartz and moganite have different crystalline structures which grow together at a fine scale in chalcedony, which is probably why it looks far less geometric than the other crystals I’ve shown. Agate is a type of chalcedony.