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Rocks: when to lick, when not to lick
Rocks: When to lick, when not to lick
Perhaps this horse has had some geologic training…. because every geologist knows that, in certain cases, licking rocks is surefire way to identify them. My beginning geology students always seem a little…hesitant…to employ their taste buds, but licking rocks is second nature for the seasoned geologist.
The best example of course is halite, the mineral commonly known as salt. To a novice geologist, halite might look a lot like quartz or calcite or gypsum, but none of these will have the distinctly salty taste, so licking it will confirm its identity. (A note to those in introductory geology classes: you’ll never miss halite on exam, if you’re willing to lick it…there can’t be that many germs on in right?)
Are there other rocks or minerals with uniquely distinctive taste? Yes; there is sylvite, a mineral closely related to halite, but with an even more pungent, disgusting salty taste. Then there are the “sticky” minerals, like chrysocolla or kaolinite (a type of clay), which make up in texture what they lack in taste. Their flavor is not distinctive but these minerals will stick to your tongue when you give them a lick—a dead giveaway.
For some rocks, licking won’t work but grinding them against on your teeth will. This is a test for distinguishing between a siltstone and a shale—siltstone will feel gritty against your teeth, shale won’t.
Are there any rocks or minerals that you should leave to your other four senses? Yes, there are, so don’t go crazy trying to get a taste of everything lithological.
Certain minerals contain poisonous elements that are not worth accidentally ingesting. For example, there’s realgar (http://on.fb.me/1e9S4b2)—a ruby red ore mineral that contains arsenic; autinite (http://on.fb.me/1JKDqjU)—a dangerous radioactive uranium-bearing mineral; the lead ores, such as galena and cerussite (http://on.fb.me/1KA7bow); and mercury ore minerals like cinnabar (it’s closeness to the word “cinnamon” is no indication of its edibility).
So for any of you just starting your geology careers…perhaps use some sensible caution, but for the most part don’t be afraid to licks the rock in your lab set. Most minerals won’t hurt you…and a little germ swap with your peers is good for the immune system. One of your greatest geologic tools is your tongue!
-CM
Photo credit: Valentina Storti http://bit.ly/1ISh4jY
(from The Earth Story FB page)
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