The WHITE ROCK vs BLACK ROCK Conundrum When you are a freshmen studying geology, a professor hands y

The WHITE ROCK vs BLACK ROCK ConundrumWhen you are a freshmen studying geology, a professor hands you a black rock and a white rock. The black rock, he/she says, is basalt. The white rock is limestone. Simple, right? Black basalt. White limestone. No problem.The same year, on a field trip, you see a black rock and a white rock, and when the professor nods at you, it’s obvious: “Black basalt, right? White limestone, right?”Several courses in petrology later, during your field mapping, you run into another black rock and white rock, scratch your head, consider the dozen sorts of lavas you now know about and sixteen varieties of limestone, then deduce: “maybe the black rock is basalt, maybe the white is limestone, I think.”By the time of your doctoral orals, out come the black and white rocks once again. You’re now a specialist in black and white rocks. “Hmmm – this black rock possibly is basalt. The white one possibly is limestone.”By the time you’re a professional geologist (if so blessed), it gets even worse. After years of experience, including mapping large areas of black micritic limestone and white hydrothermally altered lavas dating to the Precambrian, when faced with the white rock / black rock conundrum, you are now reduced to the stage of: “theoretically it’s conceivably a basalt; theoretically, conceivably, it’s limestone” as you scratch your head.And no, limestone doesn’t always fizz in acid, assuming you didn’t leave your acid bottle behind since it has a tendency to eat holes in your pockets no matter how tight you think the cap is screwed on. And I have known black lavas to fizz when they include zeolite-facies calcite in vesicles, or underlie a large limestone formation through which the percolation of ground water has introduced calcite into every fracture in the lavas…Sometimes the more one knows, the harder it becomes to be positive about anything.And that’s why we take lots of samples back to the lab even when we are confident that the black rock is basalt, and the white rock is limestone.Annie RCartoon by Vincci LauOriginal anecdote by: Prof. George Migiros, Agricultural University of GreeceSome source material:Rassios, A. and Geo-friends of the Aliakmon Legacy Project, 2008: Rocks in the Wild, IGME, Greece, 128 pp. Book, sadly, nearly out of print, a few copies left.http://www.geology.sdsu.edu/how_volcanoes_work/Unusual%20lava.html -- source link

More pics about