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Rome, Scotland, and Stake-Lined Pits

Lilia at Rough Castle (Image Credit: MB Griggs)

I was going through some old pictures the other day, and came across this image, and I was so excited that I just had to share! These may look like holes in the ground…and they are. But once, long ago they were one of the many lines of defense that the Romans used to secure the Antonine wall. Most people have heard of Hadrian’s wall, but it’s more northern cousin is less well-known. The Antonine Wall was a fantastic piece of earthen engineering built by the Romans during their very brief foray into what is now Scotland.

The Romans wanted territory in the North of the British Isles really for no better reason than, well, they wanted it. But the people that were there weren’t big fans of the Roman invasion, and eventually, after just 20 years Rome decided that it was just too much trouble to maintain a frontier border at the Antonine wall.

The Antonine wall was good while it lasted, stretching over 37 miles across Scotland. It was a 9-12 foot tall mound of dirt, with a huge ditch in front of it. There were forts along the wall almost every 2 miles, including the well-preserved Rough Castle fort near Falkirk.

Rough Castle and the Antonine Wall (Image Credit: MB Griggs)

But back to the pits, which are, in fact the best part. They were named lilia (lilies) by the Romans, who had a surprisingly wicked sense of humor (and rather strange associations with flowers). Caesar himself described them best:

“…pits three feet deep were dug, which gradually diminished in depth to the bottom. In these pits tapering stakes, of the thickness of a man’s thigh; sharpened at the top and hardened in the fire, were sunk in such a manner as to project from the ground not more than four inches; at the same time for the purpose of giving them strength and stability, they were each filled with trampled clay to the height of one foot from the bottom: the rest of the pit was covered over with osiers and twigs, to conceal the deceit. Eight rows of this kind were dug, and were three feet distant from each other. They called this a lily from its resemblance to that flower.” Caesar, Gallic Wars, VII lxxiii

The purpose of these pits was to ward off attackers from the north who really enjoyed making the Romans lives miserable. They provided an extra layer of defense to the few men who defended a crumbling, ill-defended border that was constantly under attack and poorly provisioned by a distant capital city that was too wrapped up in it’s own drama to care. Sound familiar?

Ok, Game of Thrones doesn’t have the awesome stake-lined pits at the walls, and the scottish tribes were way cooler than ice-zombies, but other than that, this is about as close to The Wall as we’re ever going to get in our world.

Antonine Wall (Image Credit: MB Griggs)

 

Five Months Without Rocks…

…makes me very sad, but it took a while to get adjusted to life after grad school. After 18 1/2 years in formal schooling, real world routines required a lot of attention. And the freelancing lifestyle does not involve a lot of free time.

But I’m baaaaack! I’m fortunate that rocks are very patient things. I offered them a peace offering in the form of an article for Popular Mechanics online about those gorgeous lava coils on Mars.

Lava Coils on Mars Image Credit: NASA/JPL/University of Arizona

To get some perspective on what a lava lake looks like here on earth, Steven Chemtob, a geologist friend, sent me these fantastic videos from the USGS of lava lakes in Hawaii: Infrared Image of Lava Lake Lava Lake

Enjoy, and I’ll have more fun rock-related posts soon! (I promise)

Topaz Tuesday

A topaz crystal Image Credit: Rob Lavinsky, irocks.com

Featured Image: http://commons.wikimedia.org/wiki/File:Quartz-Topaz-tch03a.jpg Caption: A topaz crystal Image Credit: Rob Lavinsky, irocks.com

This week’s Mineral Monday delay wasn’t due to a turkey-and-other-excellent-food-coma, whatever you may think. It’s because this week’s mineral is topaz, November’s birthstone, and I wanted to wait until my mom’s birthday to post it.

Topaz  (Al2SiO4(F,OH)2) is another silicate mineral along with kyanite, olivine, and oh, so many more. In its pure form, it is colorless and clear, and can be cut to rival diamonds.

Image Caption: The Chalmers Topaz at the Field Museum, a near-colorless 5889.5 carat topaz (Image Credit: Opacity via Flickr)

Usually, when someone refers to ‘topaz’ people think of the warm brownish-yellow common to many varieties of topaz around the world. This classic topaz color is often confused with citrine, a type of quartz.  Etymology nerds the world over are still arguing over the origin of the word topaz, with some maintaining that it came from the ancient name of an island on the east coast of Egypt, called Topazios, where the gem peridot was mined. Others maintain that the name came from the Sanskrit word tapas meaning “heat or fire.”

Like many gems, topaz comes in a wide range of colors, from blue to green to pink. But topaz is cool because it can change colors. Historically, people noticed that the vibrant colors of topaz specimens would fade over time, especially if frequently worn in sunlight.

More recently, gemstone experts realized that heating and irradiating topaz stones could cause dramatic color shifts in topaz. A blast of radiation can be fairly destructive on an atomic level. That burst can knock loose atoms within the crystal structure, and also release a few electrons in the process. If an electron fills the hole left by an atom, it can absorb certain wavelengths of light, resulting in a blue or yellow color.*

Blue Topaz Image Credit: Chris Kohtz via Flickr

Heating reverses this process, releasing the electrons, and resulting in a colorless stone.** Gemologists can use varying types of radiation and heating processes to manipulate a topaz’s color dramatically

This process has become so common that it has even affected prices for gems. There’s really no way to tell whether a stone is naturally blue or irradiated, and so blue topazes, once rare, have now become relatively inexpensive.

Happy birthday Mom!

 

*Jill Banfield at Berkeley has a great description of the process on her Gems and Gem Materials class website: here.

**Colorless, or a stone colored only with impurities instead of loose electrons. See more info here and here.

Mineral Monday: Rutile

Rutile crystals in quartz from Minas Gerais, Brazil (Image Credit: sulla55 via Flickr)

We are now almost halfway through November. Kind of shocking, isn’t it? 2011, you have flown by at far too brisk a pace.

This week’s mineral is rutile. Rutile is one of those funky minerals that is both useful and pretty, but it is usually at its best when paired with another stone or product.

Rutile is one of the natural forms that titanium dioxide (TiO2) takes. It is mined for use as a plain white pigment, and can be found in paint, toothpaste*, food coloring, sunscreen and as a coating for welding rods. Sierra Leone has one of the largest deposits of rutile in the world, and it is one of their largest exports. (Continued)

Mineral Monday: Afghanite

Afghanite from the Sar-e-Sang District in Badakhshan Province, Afghanistan. (Image credit: Rob Lavinsky, iRocks.com)

Mondays making you blue? Here’s a mineral for you.

Afghanistan isn’t exactly known for it’s great wealth of natural resources, despite the hullabaloo last year over the recently re-discovered mineral deposits in the county.

What Afghanistan does have is a mineral named after the country. Afghanite has the impossible chemical formula (Na,Ca,K)8(Al6Si6O24)(Cl2,SO4,CO3)3· 0.5H2O. It was discovered in the late 1960’s in a remote northeastern corner of Afghanistan known as Badakhshan.

Badakhshan is one of the poorest, most remote corners of the world, nestled in the Hindu Kush Mountains, and bordering both Tajikstan and Pakistan. Its one claim to fame is the mining of Lapis Lazuli, a gorgeous blue rock favored by ancient civilizations like Egypt and Rome. Afghanite was discovered in a Lapis Lazuli mine in this area, but has since been found with other blue minerals like sodalite in locales around the world.

Afghanite shares the deep blue color of Lapis Lazuli rocks, mainly because it has a very similar molecular formula to the mineral Lazurite. Both are members of the impossibly large tectosilicate mineral grouping. Tectosilicate minerals make up nearly ¾ of the Earth’s crust, and are made up of lovely little tetrahedrons of the very common elements silicon and oxygen (with aluminum subbing in for silicon just for fun).

These tetrahedrons build upon each other in predictable ways, creating a framework for the crystal structure of any tectosilicate mineral. (Tectosilicate literally means framework silicate). Afghanite, unlike other tectosilicates like feldspars or quartz is not particularly common nor useful, but it is lovely and unusual, and deserves its 15 minutes of fame.

See you next Monday!

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