A Beginner’s Guide to Licking Rocks

A geologist licking “umber”, a very dry rock which sticks to the tongue

You might be wondering why you’re being offered advice on how to lick a rock. Who licks rocks? you might find yourself asking. Well, there’s a little known species called the geologist and they are experts at said task. Some people may have heard of a geologist but most will never have seen one as they still spend much of their time in the wild. Excess facial hair, large collections of walking boots and the ability to pronounce “molybdenite” correctly are all indicators that somebody may actually be a geologist. So what are they and what do they do? They’re creatures obsessed with rocks and beer to a level beyond belief. They devote their time to volcano poking, fault finding, high-risk colouring and rock hunting, an activity in which the geologist traverses the countryside for miles and miles, risking life and limb, in the hope of locating a “fresh outcrop”. A geologist is never more than 50 yards from their geological hammer but they are not to be confused with geographers whose field weapons are typically blunt, trowels for example, and unlike geographers, geologists don’t require assistance tying their bootlaces for a day of fieldwork.

Whilst the aforementioned activities are fundamental to a geologist’s survival, probably their most favourite pastime is rock licking. This may come as a surprise to the non-geologist but it literally does mean what it says. This seemingly strange activity may seem unnecessary, dirty and demoralising to your average Joe but to a geologist, this is science! By simply licking a rock, a geologist can travel back through time to see what it was like millions of years ago, in the place where the rock was deposited. With the help of this handy guide to rock licking, you too can have the same life changing experience, you’ll be sorry you hadn’t done it sooner!

  • Hunting. The first step is to find a suitable rock to lick; you can’t just pick any old rock and expect to get the same satisfaction out of it. A good place to begin the hunt is Prebends Bridge, on the track leading up to the white gates. There is a wide choice, but avoid the coal as it has a particularly nasty taste.
  • Preparing the sample. These rocks have been there for 313 million years so they aren’t exactly what you call fresh and the bit you picked off is weathered. At this point the geologist strikes with a hammer but this is an advanced technique and not recommended for first timers. Instead, simply throwing the rock at the ground should be enough to break it open, revealing its inner beauty.
  • The first lick. Prior to the first lick the rock looks like any other but the application of a thin layer of saliva brings the rock to life. Suddenly all of the individual minerals are visible and the rock glistens in the light. Don’t worry if this doesn’t happen; it is not uncommon and it doesn’t mean you’re doing it wrong. It may be that the individual grains are too small to be seen by eye. In this case, skip step 4 and go straight to step 5.
  • Optical analysis. If the grains are visible it’s time to start measuring their size. You at least have sandstone, whose grains are defined as being at least 63 microns in diameter, ranging up to 2 millimetres. Over 4 millimetres you have pebbles and over 256 millimetres, boulders! There are many other exciting grain characteristics that can be noted. Favourites include shape, sphericity and roundness but as a beginner it is best to concentrate on grain size.
  • Lick, Chew, Swallow. Most will be excited by simply looking at the rock but only when you put it in your mouth will true satisfaction be achieved. Firstly you need to taste the rock. Secondly, chew the rock and if you’re hard enough, swallow.
  • Oral analysis. The trick here is to taste the rock and this really does require some experience so it’s likely you won’t be so successful on your first try. As a basic guide though, if the rock tastes salty it may be salt (a very logical approach) but it may also be a “sodium potassium sulphate carbonate chloride” (somewhat more difficult to follow). Other common tastes are sulphur and aluminium (you’ll know if you’ve chewed aluminium foil before). The next thing is to guesstimate the grain size. You needn’t do this if you completed step 4. If when you chew the rock it feels gritty between the teeth then the rock is a siltstone (4 – 16 microns). If the rock is smooth then it is a claystone (less than 4 microns!).
  • Christening. The intense period of data collection has come to an end. It’s now time to do what geologists fear the most, name the rock. Get it wrong and you’re fired! So what can be deduced from this seemingly pointless data? The finer the grains, the more easily they can be transported by the elements. These grains tend to reach the oceans and are only deposited when the environmental energy is so low that the wind or water cannot carry them any more. The opposite applies to coarser grains, these are deposited in shallow waters, and even rivers cannot provide the energy needed to carry these grains far from their erosional source. They are commonly deposited on meander bends where the river loses power and coarse sediments will rarely make it beyond a delta. So that’s size sorted, but with our trusty mineral identification book to hand you’ve also worked out what the grains in the rock are by looking at and tasting their properties. The composition is crucial to the identification of the rock. It’s now time to combine this information and, god forbid, christen the rock. In this frightening and unforgiving situation your best bet is to name it mudrock. Why? Over 50% of sedimentary rocks are mudrocks and the term has almost no meaning, other than it’s fine grained. Obviously don’t name it mudrock if it’s coarse grained, opt for sandstone instead, again this has little meaning so nobody can say you’re wrong. Properly naming your rock is not for the faint-hearted. There are hundreds of varieties of each rock type and geologists are finding and naming new rocks rapidly.

So what was all that for? Obviously it’s a fun pastime, it’s exciting and it’s engaging, mesmerising some would say, but what is its purpose in life? Licking rocks is not done just for fun. Evidence from the rock tells the geologist what the environment was like at the time it was deposited. For example when the rocks at Prebends were deposited, Durham was a tropical location not far from the equator, most of England was underwater and any land that was exposed was covered in dense forests. Those forests are what formed the coal. Deltas feeding from the north (now known as Scotland) brought sediment down into England and eventually terrestrial conditions were established (that’s dry land in layman’s terms). By understanding the past environment geologists are able to locate valuable resources such as oil and gold or in Durham’s case, coal! All that from one lick!

So next time you’re out and about and you see a rock, why not lick it? You have no reason not to, you might will enjoy it. Consider keeping one as a pet, take it with you wherever you go and in times of need (for you or your rock), give it a lick!

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