The "Acid Test" for lead carbonate Minerals and Carbonate Rocks

Article by: Hobart M. King, PhD, RPG

Hydrochloric mountain on limestone: This video demonstrates what happens when one autumn of dilute (10%) hydrochloric mountain is placed on a item of limestone. Protective glasses and also gloves room recommended once doing the mountain test.

You are watching: Does calcite react with hydrochloric acid

What is the acid Test?

To many geologists, the hatchet "acid test" means placing a drop of dilute (5% to 10%) hydrochloric acid on a rock or mineral and also watching for bubbles of carbon dioxide gas to it is in released. The bubbles signal the presence of carbonate minerals such together calcite, dolomite, or among the minerals detailed in Table 1.

The bubbling relax of carbon dioxide gas can be therefore weak the you need a hand lens come observe solitary bubbles slowly growing in the drop of hydrochloric acid - or therefore vigorous the a flash of effervescence is produced. This variations in effervescence vigor are a result of the kind of lead carbonate minerals present, the amount of lead carbonate present, the fragment size the the carbonate, and also the temperature that the acid.

Hydrochloric acid on limestone: This video demonstrates what happens as soon as one fall of dilute (10%) hydrochloric acid is placed on a item of limestone. Protective glasses and also gloves space recommended once doing the mountain test.


Magnesite: The mineral magnesite, which has actually a chemistry composition the MgCO3, will certainly effervesce weakly with warm hydrochloric acid and really weakly with cold acid. Specimen is around 6.4 centimeter across.

What reasons the Fizz?

Carbonate minerals are unstable in call with hydrochloric acid. Once acid begins to effervesce (fizz) ~ above a specimen, a reaction similar to the one shown listed below is acquisition place.


On the left next of this reaction, the mineral calcite (CaCO3) is in call with hydrochloric acid (HCl). These react to kind carbon dioxide gas (CO2), water (H2O), dissolved calcium (Ca++), and dissolved chlorine (Cl--). The carbon dioxide bubbles that you watch are evidence that the reaction is taking place. As soon as that occurs, calcite or one more carbonate mineral is present.

Many other carbonate minerals react with hydrochloric acid. Each of this minerals consists of one or much more metal ions an unified with a carbonate ion (CO3--). The chemistry of these reactions is similar to the calcite reaction above. The mineral reacts v hydrochloric acid to develop carbon dioxide gas, water, a dissolved metal ion, and dissolved chlorine. The reactions because that magnesite (MgCO3) and also siderite (FeCO3) are presented below.



Calcite: This transparent specimen of calcite mirrors cleavage the is characteristic of the mineral. Calcite, through a ingredient of CaCO3, will react strongly v either cold or heat hydrochloric acid. Specimen measures around 10 centimeter across.

Acid reactions of lead carbonate Minerals
MineralChemical CompositionCold acid ReactionWarm mountain Reaction
MagnesiteMgCO3very weakweak
SideriteFeCO3very weakweak
Table 1: A list of commonly and occasionally encountered carbonate minerals v their chemical formula and also reactions to cold and warm hydrochloric acid. Check results have the right to vary because of weathering, previous testing, contamination, and also specimen purity.


The Vigor of lead carbonate Reactions

Careful monitoring is important due to the fact that some carbonate minerals reaction vigorously and others barely react v cold acid.

The lead carbonate mineral the is most commonly encountered by geologists is calcite (CaCO3). Calcite is a "ubiquitous" mineral. Ubiquitous method "found everywhere." Calcite wake up in igneous, metamorphic, and also sedimentary rocks and also is the most typically encountered carbonate mineral. If you location one drop of cold hydrochloric mountain on calcite, the entire drop the acid will certainly erupt v bubbles and also a vigorous fizz will certainly last because that a few seconds.

Dolomite CaMg(CO3)2 is an additional commonly encountered lead carbonate mineral. If you place one fall of cold hydrochloric acid on a piece of dolomite, the reaction is weak or not observed. Rather of seeing an apparent fizz, you will watch a autumn of acid on the surface ar of the mineral that could have a couple of bubbles of carbon dioxide gas slowly cultivation on the dolomite surface.

However, if warm acid is placed on dolomite, an noticeable fizz will occur. This occurs because the acid and rock react much more vigorously at higher temperatures.

If you place a drop of hydrochloric acid on powdered dolomite, a visible reaction will certainly occur. This is because the surface ar area has actually been increased, making more dolomite available to the acid. (You can conveniently make dolomite powder by scratching a specimen that dolomite across a streak plate. Climate test the powder by placing a fall of hydrochloric mountain on the powder. An additional easy means to produce a tiny amount that mineral flour is to scratch the specimen through a nail.)

Different carbonate minerals have different responses come hydrochloric acid. A list of common and also occasionally encountered lead carbonate minerals is given in Table 1 with their chemistry composition and their family member reaction through cold and also warm hydrochloric acid.

When a mineral has a weak solution to acid, you must be observant and also patient to watch it. For example, magnesite has a an extremely weakreaction v cold HCl. If you powder a little amount that magnesite ~ above a streak plate and place a autumn of mountain on it, you might not see any activity for several seconds. Then, as tiny bubbles begin to kind on corpuscle of magnesite, the drop of acid will appear to thrive larger in size. That occurs as carbon dioxide is liberated from the mineral and displaces the water. Observing the formation of bubbles with a hand lens can be helpful.


Dolostone: Dolostone is a sedimentary absent composed mainly of the mineral dolomite, which has a chemical composition the CaMg(CO3)2. Dolomite will certainly effervesce weakly through cold hydrochloric acid, producing a few bubbles. The reaction is an ext noticeable when the acid is warmth and/or the rock is powdered. The specimen in the photo is around 10 centimeter across.

The mountain Test ~ above Rocks


Some rocks contain lead carbonate minerals, and also the acid test deserve to be provided to aid identify them. Limestone is composed practically entirely of calcite and also will produce a vigorous fizz through a drop of hydrochloric acid. Dolostone is a rock written of practically entirely the dolomite. It will produce a an extremely weak fizz once a drop of cold hydrochloric mountain is placed upon it, a much more obvious fizz when powdered dolostone is tested, and also a stronger fizz when warm hydrochloric acid is used.

Limestone and also dolostone deserve to be a little much more complex. Lock are periodically composed that a mixture that calcite and also dolomite and also have mountain reactions that space deceptive. A dolostone have the right to contain sufficient calcite to fool you right into calling it a limestone. For these rocks the acid test could not be enough for a i was sure identification - but at least you will recognize that the rock has a far-reaching carbonate mineral content.

Marble is a limestone or a dolostone that has been metamorphosed. It will have actually an mountain reaction that is similar to the limestone or dolostone from which it was formed.


Other Applications the the "Acid Test": Geologists have the right to use dilute hydrochloric acid to aid identify the cementing agent of sandstones. They location a autumn of dilute HCl top top the sandstone and also closely observe. If calcite is the cementing agent, one effervescence will certainly occur and some that the sand grains could be liberated. A hand lens or little microscope is provided to do the observations. The photo above is a magnified view that a item of Oriskany Sandstone, one Ordovician-age absent unit native the Appalachian basin that serves together a herbal gas reservoir and a natural gas storage unit. Oriskany sandstone is frequently cemented by calcite.


Always remember that "calcite is ubiquitous." (Ubiquitous way that it is found practically everywhere.)

Many rocks contain little amounts that calcite or various other carbonate minerals. All of these can produce a fizz even though the carbonate is only a minor component of a rock"s composition. These rocks might contain small veins or crystals of carbonate minerals that develop a fizz in call with acid. This veins and crystals can be therefore tiny that they space not clearly shows to the unaided eye. This small amount that carbonate might fizz the first time a drop of mountain is applied but be depleted and also not fizz if mountain is used a 2nd time come the same place on the rock.

Some sedimentary rocks are bound together with calcite or dolomite cement. Sandstone, siltstone, and also conglomerate sometimes have actually calcite cement the will produce a vigorous fizz v cold hydrochloric acid. Some conglomerates and also breccias contain clasts of carbonate rocks or minerals that react with acid.

Many shales to be deposited in maritime environments and also contain sufficient calcium lead carbonate to create a vigorous acid fizz. This shales were created when dirt was deposit in an environment comparable to or nearby to wherein limestone to be formed. They are composed the sedimentary clay mineral intermixed with a tiny amount that calcite. Lock are known as "calcareous shales."

Don"t enable an mountain fizz to overview the to know process. In many instances it will instead include detail come your monitoring such as: "calcareous shale" or "sandstone with lead carbonate cement." This is an useful information.


Vinegar can be used for the mountain test: Vinegar can be a safe, economical and also easy-to-obtain "acid" for identifying calcite and dolomite. Vinegar is dilute acetic mountain that produce a really weak reaction through calcite and dolomite - best observed v a hand lens.

The "Vinegar Test"

Vinegar is a dilute acetic acid systems (about 5% come 10%) that produces a weak effervescent reaction v calcite and dolomite. It have the right to be used instead of hydrochloric acid for presenting students to the mountain test. Vinegar is simple to obtain, inexpensive, and safer to usage than hydrochloric acid.The effervescence utilizing vinegar usually calls for a hand lens because that clear observation and is just observable through carbonate mineralsthat have actually a strong reaction v hydrochloric acid. Vinegar is often used when the mountain test is part of a precollege course. Safety gloves, glasses, paper towels, and also immediate accessibility to an eyewash station room recommended.


A few rocks have the right to produce an extreme reaction with hydrochloric acid. These space usually rocks created of calcite or aragonite withabundant pore an are or exceptionally high surface ar areas. Part specimens that chalk, coquina, oolite, and tufa are examples. When a fall of dilute hydrochloric mountain is placed on these specimens, an eruption of mountain foam have the right to rise up turn off of the rock and also spread come an unanticipated diameter. The reaction is very brief (and may not it is in repeatable), yet it is so sudden and also vigorous the it can surprise an inexperienced person. This description is because that one fall of acid. If more is provided an even an ext vigorous reaction will certainly occur. (These extreme reactions will certainly not occur with every specimen of this rocks. Be conscious when trial and error them or presenting them to students for testing.)

The very vigorous reaction of cold hydrochloric acid through these specimens occurs since the rocks space so porous or because they have actually a an extremely high surface ar area under a single drop of acid.


Calcite and also other lead carbonate minerals have actually a low resistance to weathering and can be assaulted by mountain in herbal waters and also soils. When testing material that has actually been exposed at Earth"s surface, that is really important to test unweathered material. A fresh surface can usually be derived by break the rock.


Some rocks space porous and contain a reservoir of air. Tiny amounts of wait escaping into a drop of acid from below can offer the illustration of a gentle acid reaction. Don"t it is in fooled. If you ar a autumn of mountain on part sandstones, a few bubbles will arise out of sharp spaces. It"s no a carbonate cement. To protect against this trouble scratch the rock throughout a streak plate and also test the powder or the grains that room produced.


The best means to learn about minerals is to study with a collection of little specimens that you have the right to handle, examine, and observe their properties. Cheap mineral collections are available in the Store.

Contamination in Mineral identification Labs

When students are offered minerals come identify, two cases can reason problems through their work.

1) In mineral identification labs, part students are ready to call any kind of mineral the produces an acid reaction "calcite" or another carbonate. However, calcite is a ubiquitous mineral and it is often current as an intimate component of other mineral specimens and rocks. This can produce a false acid reaction. To stop being misled, student should always be cautioned to check a specimen"s identity with multiple properties. If a specimen fizzes through acid yet has a Mohs hardness the seven and breaks through a conchoidal fracture, then it absolutely isn"t calcite!

Depending top top the endure of the students, specimens that are really true to your properties have the right to be presented to the class, or specimens with some challenges can be used. Lots of minerals uncovered in the ar will not be certain true come properties. It"s much better to find out that class in the lab and go right into the field with wisdom.

2) due to the fact that calcite is among the index minerals that the Mohs Hardness Scale, that is regularly used to check the hardness of mineral specimens. This can place little amounts the calcite possibly on every unknown specimen in the lab! Don"t assume that a single acid reaction is correct. Test the specimen in a 2nd location if you suspect that contamination has occurred.

In a mineral identification lab, barite is generally confused through calcite because of contamination. The barite might naturally contain little amounts the calcite, or the hardness testing of a vault student might have left little amounts the calcite on a barite specimen.Students space often attracted to an identification as "calcite" simply due to the fact that of the acid test. If the mineral exhibits a bit ofcleavage and is not very hard, then countless students will certainly arrive at an not correct identification.

Acid check Safety

Hydrochloric acid, appropriately diluted come a 10% concentration, can cause irritation if it contact the skin or eyes. The can also fade clothing. Hydrochloric acid have to kept in clearly-labeled dispensing bottles and used with quick and easy access to record towels, water, and an eyewash station. Safety glasses and protective gloves space recommended. If skin call occurs, the area have to be purged with plenty of water. If eye contact occurs, the eye must be flushed for 15 minutes with plenty that water. If a contact lens is worn, the eye must be flushed, contact lens removed, and also flushing continued. Seek prompt medical attention because that eye contact.Specimens that space tested with acid should be rinsed after testing to remove or dilute unreacted acid.

Limiting Frivolous Acid use in Labs

Most students are intrigued v the acid test and want to try it. To border frivolous mountain use, students need to be instructed to use a solitary drop of acid for the test and also to just test specimens when carbonate minerals space suspected. If that is not done, some students will usage the mountain frivolously. This habits is encouraged if the classroom is equipped with big acid bottles that are filled to the top. However, if the mountain bottles are little and virtually empty at the beginning of class, students commonly ration their use of the acid to ideal amounts. Small, nearly empty bottles makes much less acid obtainable to spill.


Acid dispensing bottles: little acid dispensing bottles job-related well because that the mountain test. Castle dispense the mountain one-drop-at-a-time and will no spill if they space knocked over. If you space a teacher supervising the mountain test in a classroom, provide students small bottles the are virtually empty. The will alleviate the lot of frivolous acid usage that could otherwise occur. Brand the bottles clearly and instruct students in acid use before making castle available.

Acid party Selection

The type of party selected for dispensing the mountain is important. Activities supply stores sell bottles that space designed for dispensing acidone-drop-at-a-time. The lid is constantly on these bottles (except as soon as they are being cleaned or refilled), and they carry out not produce a pour out whenthey space knocked over. Bottles v a removable lid that has actually a squeeze pear dispenser will certainly be sometimes knocked over as soon as the lid is offif they are being used by regular humans.

Acid dispensing bottles need to be do of rigid plastic through a little opening which permits acid come be easily dispensed one-drop-at-a-time. Soft dispensing party or bottles with a bigger opening deserve to dispense a huge amount the acid through an inadvertently squeeze.

Sources of Hydrochloric Acid

Hydrochloric mountain diluted to a 10% systems cannot it is in purchased in most communities. The ideal place to acquisition commercially all set solutions is from a laboratory supply company. Purchasing it ready-for-use is the recommended means to achieve it. Don"t shot to prepare your very own solution if girlfriend don"t know precisely what you room doing and have an equipped laboratory. Your chemistry room might have the ability to assist you with ordering acid. Part generous chemists will prepare a 10% solution for you.

Mineral Specimens as "Consumables"

Mineral specimens the are offered properly in the science classroom or activities will must be replaced frequently.Students will certainly be investigating them through hardness tests, streak tests, mountain tests and also other experiments. Every one of thesetests damages the specimen and make it much less fit because that the next group of students. To save the mountain test indigenous fouling your entire collection, questioning students to rinse specimens after testing with acid and limit experimentation to only when it is needed.

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