C is for Cactolith

| Published on March 1, 2010

C is for Cactolith

Geologic jargon — though handy for triple-word scores — should be used in moderation.

By Bill Langer

Cactolith (noun) — a quasihorizontal chonolith composed of anastomosing ductoliths whose distal ends curl like a harpolith, thin like a sphenolith, or bulge discordantly like an akmolith or ethmolith.


Way back when I was first married, I casually dropped the word cactolith to my young bride, Pam, to let her know that her work to put me through graduate school was well worth the effort. I failed to impress her.

The term cactolith and its associated definition were created by Charles B. Hunt, a U.S. Geological Survey (USGS) geologist, and published in Geology and geography of the Henry Mountains region, Utah (1953). While Charlie was, in fact, describing an actual geological feature — an intrusive body of rock that resembles a saguaro cactus — he was also taking a satirical jab at what he saw as an absurd number of “-lith” words cropping up in the geological literature by using five other “-lith” terms in his definition. To his amazement, the USGS reviewers did not catch on, the report was approved, and cactolith became part of the geologic jargon.

Even though I try not to use geologic jargon in my articles, I do find times when its use is appropriate. What could be better than laying down “xenolith” on a triple-word score for 54 points and being able to say to Pam, “Yes, it really is a word.” Now that would impress her.

Practically everyone who has taken a basic earth science course gets a kick out of throwing around a little jargon. “That’s not gneiss (pronounced nice).” Or, “I took it for granite.” And, “That’s tuff (a volcanic rock).” Finally, “I lava volcano.”

scrabbleWe all picked up some jargon in grade school when we learned that stalactites (stalasso, which is Greek for drip) hold tight to the roof of a cave, and stalagmites (stalagma, which is Greek for drop) grow from the floor of the cave and might meet up with the stalactite. And some real common place jargon comes from deinos, which is Greek for terrible, and sauros, meaning lizard. What is a terrible lizard? A dinosaur, of course.

Some geologic jargon is self descriptive. Limestone originally referred to stone that could be used to make lime. Pillow lava looks like a pile of pillows. Columnar basalt forms grand columns. Hogback hills resemble the back of a hog. Star dunes are sand dunes that form in the shape of a star. The channels of braided streams converge and diverge like the strands of a complex braid. And you can probably picture serpentine, a rock with mottled shades of green, like the markings on a snake. Some folks like the names of gems, rocks, and minerals so much that they give them to their kids; Amber, Beryl, Crystal, Flint, Jade, Opal, Pearl… the list goes on.

Some geologic jargon just sounds pretty, like Rapakivi. We have Rapakivi granite (marketed as Baltic Brown) countertops in our kitchen. It is a beautiful dark rock consisting of marble-sized, salmon-colored orthoclase feldspar ovoid masses mantled with thin off-white plagioclase feldspar rims, floating in a black hornblende-biotite groundmass.

Oops, there I go, resorting to geologic jargon. Please forgive me, I am a geologist and can’t help myself. It’s not my fault…


Bill Langer is a geologist with the Mineral Resources Team of the U.S. Geological Survey and can be reached at 303-236-1249 or via e-mail at blanger@usgs.gov.

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