Corundum Crystals: A sapphire is a sapphire is a sapphire is a… ruby?

The name Sapphire etymologically is a late 13th century word derived from old French (Saphir), which in turn derives from Latin (sapphirus), which came from Greek (sappheiros), but it ultimately originated from Semitic (sappir). Some linguists propose an origin in Sanscrit (sanipriya) but they’re not entirely sure.

Sapphires have been prized for both their hardness and their color. On the Mohs scale (a ten point scale), where diamonds are a ten, corundum crystals are approximately a 9.


When you think of a sapphire, what color do you think of? Blue? Most people do, but not all sapphires are blue. Corundum crystals of gemstone quality in any color other than red are called sapphires, while the red ones are called rubies. The colors we see when we look at corundum crystals are all the result of impurities in the crystals. An intensely blue sapphire is the result of titanium and iron in the corundum crystal. A ruby is red due to the presence of chromium.

A clear corundum crystal contains a repeating unit of aluminum oxide and no other impurities (less than a few hundredths of one percent of titanium anyway). Therefore, if any corundum of color, besides red, is a sapphire, then would a clear gem be called a sapphire or something else?



Now, rubies and their color can be explained by crystal theory but sapphires and their colors cannot. Sapphire colors are the result of a process called charge transfer. Specifically, intervalence charge transfer or cooperative charge transfer, which is the transfer of one electron from a transition-metal ion to another.

Below is all of the science gobbly-gook to go along with this concept.

“Iron can take the form Fe2+ or Fe3+, while titanium generally takes the form Ti4+. If Fe2+ and Ti4+ ions are substituted for Al3+, localized areas of charge imbalance are created. When Fe2+ and Ti4+ ions occupy two adjacent sites in a corundum crystal, the transfer of an electron from the iron cation (positively charged) to the titanium cation (positively charged) can now change the valence state of both.

Fe2+ + Ti4+ -→ Fe3+ + Ti3+

This occurs because there is enough overlap between the outer orbitals of Fe2+ and Ti4+ to allow an electron to pass from one ion to another. This process requires energy.

Intervalence charge transfer is a process that produces a strong colored appearance at a low percentage of impurity. While at least 1% chromium must be present in corundum before the deep red ruby color is seen, sapphire blue is apparent with the presence of only 0.01% of titanium and iron. This energy jump is comparatively easy for electrons to achieve when light shines on the crystal. Charge-transfer transitions are strong because they are "allowed" by quantum considerations. The "forbidden" transitions in the ligand field-colored ruby are much weaker.

Sapphires undergo "heteronuclear" charge transfer as electrons are transferred between ions of different elements.

When the ions belong to the same element, homonuclear charge transfer occurs. A common example is the transformation that occurs in iron (Fe). The surrounding environments of the two iron ions have to be different.

FeA2+ + FeB3+ –→ FeA3+ + FeB2+ (electrons transferred from site A to site B)”


Random tid-bit:

A unique “orangy-pink” sapphire is labeled padparadscha, which means “lotus flower” in Sinhalese (the language spoken in Sri Lanka). Sri Lankans have a special affection for the color that’s traditionally been linked with their country.

Other uses for corundum crystals, besides being pretty:

Corundum crystals are manufactured for industrial or decorative purposes in large crystal boules (a boule is a single-crystal ingot produced by synthetic means). The crystals have been found useful for, and are created for, many industrial purposes. Synthetic sapphires are used in shatter-resistant windows, military body armor, scientific optical windows, and much more.

The scientific community prizes synthetic sapphires for their use in optical windows. They offer a wide optical transmission band from UV to near-infrared, are stronger than other optical materials or standard glass, highly resistant to scratching or abrasion, have an extremely high melt temperature (2030 degrees Celsius), are completely unaffected by all chemicals except some very hot caustics and fluorides, and they are the hardest natural substance next to diamonds.



The crystals are also made into sapphire wafers to be used as an insulating substrate in high-power, high-frequency CMOS integrated circuits. This type of circuit is referred to as an “SOS”, or “silicon on sapphire”, chip. The sapphire wafers are used because of their low conductivity for electricity and their high conductivity for heat. This means that the sapphires act as a good electrical insulator while helping to conduct heat away from the high-heat producing circuit.



Also due to the hardness of sapphires, they are used in the watch industry. Wristwatches can be found to have sapphire crystals and movement bearings in them.

OK, so there is a good bit of information for you to start with. You should have plenty of questions to go out into the world and continue learning more for yourself. Like what other interesting materials you might find inside common items like the watch you wear everyday?

What will I post about next? Probably not your wristwatch... but hopefully something else you'll find interesting!

References and Further Reading:

http://www.webexhibits.org/causesofcolor/index.html
Minerals: Their Constitution and Origin
     By Hans-Rudolf Wenk, Andrei Bulakh
http://www.etymonline.com/index.php?term=sapphire
Gemstones: Properties, Identification and Use
      By Arthur Thomas
www.Gia.edu
Sapphire: Material, Manufacturing, Applications
      By E. R. Dobrovinskaëiìa, Leonid A. Lytvynov, V. V. Pishchik
http://www.gemresearch.ch/certs/report/auctrep2.htm

Glaucus Atlanticus

     Yes, this critter is real… and dangerous.

     Also known as the sea swallow, blue glaucus, blue dragon, blue sea slug, blue ocean slug, and, more recently, the real life pokemon. Glaucus Atlanticus is found throughout the tropical Atlantic, Pacific, and Indian oceans. This Glaucus is a type of nudibranch, a shell-less mollusk known for their extravagant shapes and colors. A normal sized one averages around three centimeters in length.

     According to the natural history museum, I gleaned the following details about this little blue oddity of the sea.

     The Blue Glaucus is the only species in its genus, “Glaucus”, and one of only two species in the entire family of “Glaucidae”. They float upside down by swallowing air and storing it in their stomachs. And speaking of their stomachs, their primary food is made of hydrozoans (including the Portuguese Man O’ War).  Not only do they eat them, but they store their food’s stings in their own little frilly fingers. Since they collect them instead of creating them, they can actually be more deadly than a Man O’ War.

     In other words, they may be small, they may be pretty, you may want to touch them… DON’T.

     Those frilly little fingers are called cerata. Every Glaucus Atlanticus has up to 84 of them. These fingers hold onto the nematocysts (the stings from the jellyfish it eats) in specialized sacs called cnidosacs.

     Earlier, I said that there was another Glaucus in the family, it is called Glaucilla Marginata. The Marginata has more cerata, up to 137 in total. The Marginata also has a longer tail than the Atlanticus, even though it is actually the smaller of the two. Marginata only reaches 12mm in length compared to Atlanticus, which can grow several centimeters.  (I believe eight centimeters is the largest recorded, but I am still looking for confirmation on that.)

     I’m feeling like some space knowledge today. So, let’s talk about Mercury. No, not the stuff in thermometers. As you’ll notice, I don’t have sources cited. This is because I have compiled information based on many sources, cross-referenced and triple-checked to be sure everyone agrees. Unlike the general idea of how many planets there are in our solar system. I know people disagree, that’s why what I have put below is pretty much just the bare-bones about Mercury. Yes, this is elementary, get over it.

     Mercury is one of the smallest planets and the closest to the sun in our solar system. The orbital period for mercury is only about 88 earth days. Mercury is approximately 35,980,000 miles (57,910,000KM) from the sun. It has a radius of 1,516 miles (2,440KM) and a density of 5.43 g/cm³. Its mass is only 0.055 Earth masses and has a surface area of 28.88 million square miles (74.8 million KM square). Compared to Earth, the length of a single day on Mercury lasts 58 days, 15 hours, and 30 minutes. It travels around the sun faster than any other planet in our solar system.

 (Photo from generic Google search)

     Mercury has almost no atmosphere and its dusty surface resembles the moon. The surface is composed of a dusty layer of minerals, like silicates, which create plains, craters, and cliffs. Dust aside, Mercury is a heavy planet. As the sun formed, it pushed many of the lighter elements away, leaving the heavy elements to create the inner planets. As a result, Mercury is composed primarily of heavy elements, like iron, with the silicates just forming the outer crust. This crust is only about 300-400 miles thick (500-600KM)

     Due to the thin atmosphere, a thin mixture of 95% helium and hydrogen, mercury alternates between freezing and boiling. The sun-side reached 950 degrees Fahrenheit (510 degrees Celsius) while the dark side can get as cold as negative 346 degrees Fahrenheit (negative 210 degrees Celsius).

     The gravitational pull on Mercury is less than that of Earth. If you traveled to there, you would weigh only 38% of what you weighed on Earth. So there you go, no more need to diet, just go to Mercury and you'll lose 62% of what you currently weigh! 

     OK, so now that we're done with our elementary astronomy lesson, what shall we learn next? 

Obviously, something that has nothing to do with mercury, or space, or anything that would logically follow this post. Enjoy!