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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 that defines some minerals and is fun. Some minerals have a well-distinct taste, and liking can solve identification questions quickly. 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.

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

If you want to check out the best books about rocks and minerals identification, you can find them here (Amazon link).

Do Geologists Lick Rocks?

While it may seem peculiar, geologists have a surprising method for quickly identifying certain rocks and minerals – they lick them! This strange approach is a useful tool for express identification in the field.

Geologists often resort to licking rocks and minerals, particularly when dealing with evaporite minerals such as halite, sylvite, gypsum, and calcite. This practice proves especially handy for distinguishing between halite (common salt) and sylvite minerals, as their salty taste is a dead giveaway. Additionally, licking can help differentiate between siltstone and shale rocks, providing valuable insights into their composition and characteristics.

Why Do Geologists Lick Rocks?

One of the main reasons why geologists employ the technique of licking rocks is for mineral identification, particularly when it comes to a specific group known as evaporites.

Evaporite minerals share similarities in appearance and hardness, making them challenging to differentiate visually. Licking provides a rapid and effective method for identifying certain mineral species within this group.

By tasting the mineral, geologists can quickly determine its identity. For instance, halite (common rock salt) and sylvite have a distinctive salty taste, which sets them apart from other minerals. Similarly, minerals like chrysocolla or kaolinite (clay) may adhere to the tongue, offering further clues to their composition.

Moreover, licking rocks can serve additional purposes beyond identification. It can help geologists moisten the rock surface, making it easier to examine and analyze. This practice is especially useful when working with evaporites, where the texture and taste of the minerals can provide valuable information.

It’s worth noting that licking rocks as a method of mineral identification is safe and commonly practiced by geologists. In fact, many of us unknowingly perform a similar test every day without realizing it! Common table salt, known to geologists as halite, is a prime example of an evaporite mineral.

Evaporites, broadly classified as chemical sediments precipitated from water following the evaporation and concentration of dissolved salts, encompass a variety of minerals.

Some of the principal evaporite minerals include:


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


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


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

Halite (NaCl) is the best-known mineral, and it is a table salt we use daily. That’s why the taste of salt helps geologists quickly differentiate halite from the bulk of minerals. 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 from others.

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

TIP: Moonstones are rocks that you would like to try to 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. There’s 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 to touch the sample with the 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, washing your hands after contact with them is highly recommended. 

Mineral nameFormulaCharacteristic
GalenaIt is a toxic antimony sulfide mineral with a distinct metallic luster.Is 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.
StibniteSb2S3It is an iron arsenic sulfide with a brilliant steel metallic color.
OrpimentAs2S3It is an arsenic sulfide mineral with a stunning orange-yellow color. All forms of arsenic are a serious risk to human health.
Arsenopyrite FeAsSIt is a form of arsenic sulfide with thallium and lead. The thallium inclusion in this arsenic sulfide combines two extremely dangerous and deadly minerals.
HutchinsoniteIt is a dangerous mineral composed of hydrated green copper, phosphate, and uranyl. (Tl, Pb)2As5S9
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 that should not be licked

TIP: The mineral’s color 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

I still have not found the answer to your questions 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 has no 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 galena particles can be easily separated. So please avoid licking galena, ingesting galena particles, and inhaling 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, but the taste will always be salty.

Can I Lick Gypsum?

Sometimes, gypsum looks very similar to halite. They 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.

Recommendation box: All tools and equipment you need for rockhounding and rock identification* (Amazon links):

1. Estwing Rock Hammer – Light, comfortable, and extremely durable hammer.
2. Estwing Geologist Pick – Classic and the most trusted paleo pick in the world.
3. Finder 12-inch Chisels – Heavy-duty chisels set with hand protection.
4. Mini Handle Shovel – This is a great tool for digging deep in the dirt.
5 Ironclad Utility Work Gloves – Breathable, but they also protect the areas requiring them most.
6. 3M Safety Glasses – Comfortable and efficient goggles for rockhounding.
7. Convoy 8+ UV Light – 365nm UV LED flashlight with a patented glass filter.
8. Wesley’s Jewelers Loupe – High magnification options (30X and 60X) with carrying case.
9. Mohs Hardness Kit – A specially designed kit for rockhounds

*All recommended products are personally tested and regularly used by experts from this website.


Licking rocks and minerals in geology is about fun and 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 arsenic, lead, mercury, antimony, thallium, uranium, and copper.

PS: To learn more about our expert Olena’s research, visit her Instagram account, GPMinerals_Org.

TIP: Another great option for identifying rocks and minerals is using a 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)