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Licking Rocks in Geology: Why & How (Answered by Geologist)

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Licking rocks and minerals in geology is a common practice to define some kind of minerals and, of course, a bunch of fun. Some minerals have a well-distinct taste, and liking can solve identification questions in a second. But be careful. It is not safe to lick any rock because some minerals are toxic. Avoid licking bright colored yellow, orange, red, and green minerals.

Licking the rocks and minerals is used to define some particular minerals. Halite, commonly known as salt, and sylvite can be easily identified by licking because of their salty taste. Licking rocks can help to distinguish halite and sylvite from visually similar quartz, calcite, and gypsum.

Geologists lick rocks! Even more, we were taught to do it during our classes! There is a group of similarly-looking white, semi-transparent minerals like quartz, calcite, gypsum, halite (salt), and sylvite, and licking will save us a lot of time to separate halite and sylvite.

If you are interested in checking out the best books about rocks and minerals identification you can find them by clicking here (Amazon link).

Do Geologists Really Lick Rocks? Here's Why and How
Do Geologists Really Lick Rocks? Here’s Why and How

Do Geologists Really Lick Rocks?

It may seem strange, but geologists really licking some rocks and minerals. This is a useful express identification method for some kinds of rocks and minerals.

Geologists really lick some rocks and minerals. Especially when they are working with evaporite minerals (halite, sylvite, gypsum, calcite). Licking helps geologists to identify halite (common salt) and sylvite minerals because of their salty taste and to differentiate between siltstone and shale rocks.

Why Do Geologists Lick Rocks?

The main reason why geologists lick rocks is the identification of minerals. Licking helps geologists with identification of a very particular mineral group of evaporites.

Minerals of that group look similar and have the same hardness, so licking is a prompt way to identify some mineral species.

Licking helps geologists to identify some rocks and minerals quickly or to moisten the rock surface to see it clean and fresh. For example, halite (common rock salt) and sylvite have a salty taste. Some minerals like chrysocolla or kaolinite (a type of clay) will stick to the tongue. 

Geologists usually use licking tests while working with evaporites. It is absolutely safe. Even more, you do the same test every day! Surprised? Of course! Common table salt is also a mineral known to geologists as halite and belongs to evaporites.

Evaporites are chemical sediments precipitated from water following evaporative concentration of dissolved salts.

Principal evaporite minerals  are classified into:

Carbonates 

  • Calcite (CaCO3)
  • Dolomite (CaMg(CO3)2)  
  • Magnesite (MgCO3)

Sulfates 

  • Gypsum (CaSO4·2H2O)  
  • Anhydrite (CaSO4

Chlorides

  • Halite (NaCl) 
  • Sylvite (KCl)
  • Carnallite (KMgCl3 · 6H2O)

Halite (NaCl) is the best-known mineral as it is a table salt we use every day. That is why the taste of salt helps geologists to differentiate halite from the bulk of minerals very quickly. Halite has a distinct salty flavor.

Sylvite is another evaporite mineral of the composition – (KCl). Structurally it is similar to halite. Sylvite crystals are often orange to red. It is the chief source of potassium. Its principal use is as a potassium fertilizer. Sylvite has a salty taste with a distinct bitterness.

While it seems like it should be easy to tell halite and sylvite apart, they both have a wide range of colors they come in. Himalayan rock salt, for example, is usually halite but often visually resembles sylvite more closely.

With the help of the licking test, you will easily distinguish these two minerals and differentiate them from other evaporites, like calcite, magnesite, dolomite, gypsum, and anhydrite.

The other reason to lick rocks is grain size differentiation. It’s challenging to compare grain size with the naked eye. Fingers and touch tests often aren’t quite sensitive enough to feel the differences; however, your mouth is!

You can tell the difference between siltstone and shale (clay-sized material) easily: siltstone will feel gritty against your teeth, while shale won’t.

The last reason for licking rocks is the ability of porous rocks and minerals to stick to the tongue. Chrysocolla (a hydrated copper silicate mineral) and kaolinite (clay mineral) can be identified this way.

Chrysocolla can be confused with azurite or turquoise. Kaolinite – with a bulk of fine-grained white stones (magnesite, aragonite, diatomite, etc.). A licking test will easily differentiate these two minerals among others.

BTW: Do you want to know more about rocks and minerals identification? The books listed below are the best ones you can find on the internet (Amazon links):

TIP: Moonstones are definitely rocks that you would like to try lick. And even more when they are tumbled. Find out more about tumbling moonstones in the article below:


Can You Tumble Moonstone? Try These 4 Simple Steps


How Do Geologists Lick Rocks?

Geologists have some unofficial rules while licking rocks. It is just a moment’s touch of the sample by the tip of the tongue only. No need to cover the whole rock.

Also, geologists lick only light-colored semi-transparent rocks and avoid any bright-colored or metallic luster ones.

Licking rocks doesn’t mean any long process. It is enough just to touch the sample with a tip of the tongue to make all the necessary tests and to identify the mineral. Moreover, it is dangerous to lick any rock as many of them are toxic and poisonous. Do not lick bright yellow, orange, and red minerals.

Don’t lick anything bright orange, red or yellow minerals. These intensely colored minerals or minerals with distinctive metallic luster usually have poisonous chemical elements, like arsenic, lead, mercury, antimony, thallium, uranium, and copper.

Here is a table with highly toxic minerals which should not be licked. Also, it is highly recommended to wash your hands after contact with them. 

Mineral nameFormulaCharacteristic
GalenaPbSIs a lead sulfide with a metallic luster. The lead in galena is toxic if inhaled or ingested from dust particles.
CinnabarHgSThe bright scarlet mineral of mercury(II) sulfide. Mercury is highly toxic to humans.
StibniteSb2S3Is a toxic antimony sulfide mineral with a distinct metallic luster.
OrpimentAs2S3Is an arsenic sulfide mineral with stunning orange-yellow color. All forms of arsenic are a serious risk to human health.
Arsenopyrite FeAsSIs an iron arsenic sulfide with a brilliant steel metallic color.
Hutchinsonite(Tl,Pb)2As5S9Is a form of arsenic sulfide with thallium and lead. The thallium inclusion in this arsenic sulfide combines two extremely dangerous and deadly minerals.
AutuniteCa(UO2)2(PO4)2 · 10 – 12H2OA hydrated calcium uranyl phosphate, a uranium-bearing mineral of bright-green color.  Licking radioactive elements is very dangerous.
Torbernite Cu(UO2)2(PO4)2 · 8 – 12H2OIs a dangerous mineral composed of hydrated green copper, phosphate, and uranyl. 
Chalcanthite CuSO4·5H2A hydrated water-soluble copper sulfate. The mineral is easily water-soluble and can cause copper contamination.
List of highly toxic minerals which should not be licked

TIP: The color of the mineral determines whether the geologist can lick it. Find out more about rock colors in the article below:


Rock Colors: What Determines Color & Why Different Colors


FAQ About Licking Rocks and Minerals

Still did not find the answer to your answers about licking rocks and minerals in Geology? Find frequently asked questions in the section below:

What Happens If You Lick Rose Quartz?

Nothing will happen. Quartz doesn’t have any taste, so you will only feel like you touched a glass. Quartz is extremely hard (7 on the Mohs scale) and absolutely doesn’t have any specific taste. But if you are trying to bite a sandstone (a rock composed of quartz), it will creak.

What Happens If You Lick Malachite?

It is dangerous to lick malachite as it is toxic if inhaled or swallowed. Malachite is a copper carbonate hydroxide mineral. Other copper compounds have been used in pesticides and fungicides for decades. Malachite doesn’t have any specific taste and can harm health if ingested. 

What Happens If You Lick Galena?

Do not lick galena as it is a highly toxic lead mineral. Galena is a lead sulfide mineral. It is very soft and brittle, so microscopic particles of galena can be easily separated. So please, avoid licking galena, ingesting galena particles, and inhalation of galena dust.

Can I Lick Halite?

Halite is the mineralogical name of ordinary kitchen salt, so you know the taste of halite for sure. For that very reason licking halite is one of the diagnostic features. Halite can occur in white, yellow, pink, and even blue colors, but the taste will always be salty.

Can I Lick Gypsum?

Sometimes gypsum looks very similar to halite. They both have similar colors, transparency, luster, streak color, and hardness. Liking can help you to differentiate these two common minerals very quickly. Gypsum doesn’t have any taste, but halite has a distinctly salty taste.

Conclusion

Licking rocks and minerals in geology is not only about fun but also about the rapid identification of some kind of rocks and minerals.

There are the most common reasons for leaking rocks and minerals in geology:

  1. To identify halite (common rock salt) and sylvite due to their salty and bitter taste respectively.
  2. To identify chrysocolla or kaolinite (a type of clay) because they both stick to the tongue.
  3. To differentiate between siltstone and shale rocks. Siltstone will feel gritty against your teeth, shale won’t.
  4. Moisten the sample to see a fresh surface (observe real color and luster).
  5. To amuse people around 🙂

Geologists know that it is forbidden to lick bright-colored (yellow, orange, red, green, and blue) minerals and metallic luster minerals.

These minerals can be toxic because of the presence of arsenic, lead, mercury, antimony, thallium, uranium, and copper.

PS: If you want to know more about our expert Olena’s research, visit her Instagram accout GPMinerals_Org.

TIP: Another great option how to identify rocks and minerals is using an UV light. If you want to know more about rockhounding with UV light check out the article below:


GUIDE: Rockhounding with UV Light & 3 Best UV Lights (2021)