siliceous and apache tears and obsidian and phenocryst and porphyritic

Ever since September 11, 2004 (not 2001), I have not been able to get siliceous out of my mind. It sounds or seems to rhyme with words suggesting sexual matters (salacious or lubricious), but the potentially suggestive sexual context is not what has kept it in my mind. In short, it was the word I screwed up on in the National Senior Spelling Bee to gain second place to Professor Jeff Kirsch of the University of Wisconsin. He knew the word; he told me it was on all the "specialized word lists" that those who have had experiences in spelling bees study (Jeff had placed high in the kids Spelling Bee 39 years ago). Unfortunately I was not a speller who did anything more than study the dictionary for several weeks prior to the competition in order to supplement my general knowledge. I was pleased, however, with my second place showing; indeed, my participation in the tournament stimulated these pages on words. I know that if I ever get siliceous again in a contest, I will hit it out of the park instantly.

So, when I got siliceous (which, by the way, means derived from or made up of sillicon) wrong, I was terribly embarrassed. I think I had seen the word previously, even if it had not been part of my regular vocabulary. But now, as I am studying gemology/geology I am beginning to run into the word wherever I turn. It is as common to geologists as eschatology is to theologians. I remember saying to myself, "This word is EASY!" and then berating myself even further. Yet, the result of my blowing the word has been to open up many words that I otherwise might never have learned. Those who say that defeat is much better for us at times than victory may be right. Those who lose sometimes have a strong motivation not to lose again or, alternatively, not to lose in the same way again. But, in the final analysis, my study of words now is not for the purpose of spelling them better; my study is to enlarge my horizons and, in the process, learn to spell them.

The Uses of Siliceous

The word siliceous appears most frequently in geology in the phrase "siliceous glass." Obsidian is the most familiar of such siliceous glasses. Obsidian is not a mineral because it has no crystal structure. It usually appears in black to dark brown to grayish brown hue. Obsidian is a remarkable stone, with a vitreous luster, appearing in varieties known as "mahogany obsidian," "rainbow obsidian," "gold-sheen obsidian," or, most striking, "snowflake obsidian." In the last there are inclusions of white, gray or sometimes red spherulites (small spheres), which give the apperance of snowflakes on a black background.

The dark gray or black, pebble-sized nodules of obsidian are known as apache tears. One web site comments that this name was apparently based on American Indian lore in which these masses were said to have been formed in the face of cliffs when Apache warriors jumped to their death rather than being captured by their pursuers. Thousands of these "staring black eyes" peep out from gray flaky lids in the caves of Superior, AZ. Nature, as it were, was weeping when its braves were forced over the cliffs to their deaths.

Obsidian which has this snowflake pattern may fracture quite easily (it does not cleave because there is no crystal pattern), and when it does so it might release such internal pressure that the entire stone can crumble. How illustrative of the human condition--when some of us are "scratched" or "fracture," we become like powder.

Igneous rocks are always siliceous and the type of igneous rock in which obsidian is found is usually rhyolite. While we are learning new words, we might as well learn that obsidian often comprises phenocrysts, too. A phenocryst is "a conspicuous, usually large, crystal embedded in porphyritic igneous rock." A porphyritic rock is one in which large crytals are set on a matrix of finer-granied crystals or of glass.

Tektites

One of the more fascinating examples of siliceous glass is the tektite. Tektites, also known as Moldavite (because of their discovery near the Moldau River in Czechoslovakia) are glass globes typically less than 2 inches in their greatest dimension that are strikingly aerodynamic in appearance, which has led to the theory that they appear to be liquid drops that hardened and picked up more liquid as they moved through the air. They are colorless, green, yellowish green, brown, gray or black. The regnant theory for a long time was that tektites were to be differentiated from meteorites in that the former were witnessed plunging to earth but no one knew where tektikes came from or who they ended up on earth. Hypersonic airflow combined with rapid cooling left interesting grooves in the tektites and shaped them into form such as buttons, dumbells, disks and teardrops. Tektites have been found in seven locations in the world, taking their name from the Czech location, and the locations make a large "S" shape when you study a map. Thus, the theory for a long time was that tektites, which are also not minerals, rell to earth at the same time.

Another approach would argue that the tektites were the product of collision of the extraterrestrial projectile with rocks on earth or, more visually, they are the "splash" caused by the dropping of the tektite on the earth. A more recent hypothesis is that tektites represent "moon splash,"--volcanic eruptions of the moon ejecting various forms of this siliceous glass to earth.

Conclusion

One of the reasons I was beating myself up after the tournament was that I realized that siliceous was a common word in geology because silicon is one of the commonest elements on earth. Silicates are formed most frequently when silicon combines with one of the following seven elements (in order of frequency): Oxygen (O), Aluminum (Al), Iron (Fe), Carbon (C), Potassium (K), Sodium (Na) and Magnesium (Mg). I don't suppose I will ever again misspell siliceous, and now I even have a context for it!