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Real calcite is a unique mineral with exclusive properties, which makes them easily distinguishable from fakes. Real calcite is a very common mineral. It occurs in all types of rocks and in a very wide range of environments. As calcite is so common, it usually doesn’t have synthetic fakes. In most cases, some other natural minerals can be mistakenly called calcite. Let’s make it clear today! Be ready! We are going to do a lot of experiments today!
The main difference between real and fake calcite is the real calcite double refraction phenomenon; its rhombohedral crystal form and perfect cleavage in three directions. Real calcite will react with weak acid, while other mineral fakes will stay inert. Also, real calcite glows under UV light.
Let’s do some experiments today! Be ready to discover an optical phenomenon of the transparent real calcite. We will describe the chemical reaction between real calcite and acid. Fakes are not competitors to real calcite. We will spot fakes easily together!
If you are interested in checking out the best books about rocks and minerals identification you can find them by clicking here (Amazon link).
How To Tell if Calcite is Real?
To tell if calcite is real or not, it’s necessary to conduct some simple experiments. But let’s have a look at real calcite. What are the typical colors and crystal forms? What are the associating rocks and minerals? What are the main properties of real calcite?
Real calcite has a list of unique features that will let you distinguish it from other minerals. Real calcite has three cleavage planes and none at the right angle, which means calcite will look rhombohedral and never cubic. Calcite reacts vigorously with hydrochloric acid and weak acids like vinegar.
Real calcite (CaCO3) occurs in all types of rocks (igneous, metamorphic, and sedimentary) and is the most commonly encountered carbonate mineral.
Calcite ranges from transparent to translucent. Colors may be colorless, white, cream, pale yellow, yellow-brown, brown, and even bright pink or red due to impurities.
Real calcite can be found in a variety of forms. I can be drusy, pisolitic, stalactitic, stalagmitic, prismatic, acicular, tabular. Calcite crystals of scalenohedron and rhombohedron form are most common.
Calcite may be contacted and twinned; may also be cryptocrystalline, with no visible crystals or coarsely crystalline to big magnificent monocrystals.
Real calcite is the primary mineral in both marble and limestone. It occurs with dolomite, quartz, gypsum, barite, fluorite, pyrite, sphalerite, galena, chalcopyrite, danburite, stilbite, malachite, and azurite. Some of them can be mistakenly diagnosed as calcite and be considered fake calcite.
The best and the fastest way to tell if calcite is real is to place one drop of cold hydrochloric acid on calcite. The entire drop of acid will erupt with bubbles, and a vigorous fizz will last for a few seconds.
How Does Real Calcite Look Like?
As we can see from the previous passage, real calcite occurs in a wide range of colors and forms. Let’s have a closer look at it and find out the specific features that will help us to recognize real calcite visually.
Real calcite occurs in a variety of colors, even a bright pink because of impurities, but in most cases, it’s white and creamy colors. The crystal form is rhombohedral. Real calcite cleavage is perfect in three directions, so you will never observe right angles. The luster is glassy to resinous and dull.
Real calcite has the next characteristics:
- Color: usually white or colorless but sometimes are found in light pastel colors
- Crystal form: rhombohedral
- Luster: glassy to resinous.
- Streak: white
- Hardness: 2.5 to 3 on Mohs Hardness Scale
- Cleavage: Perfect in three directions
This exceptionally clear calcite is known as Iceland Spar. It is an excellent example of the rhombohedral cleavage of calcite (three cleavage planes, none at right angles). Also, it shows how you can see the double vision when you look through 2 of 3 sides of a calcite rhomb.
The calcite is readily identified by its rhombohedral cleavages. The non-90° angles between the cleavage planes will tell you that it’s real calcite.
Looks can be deceiving, and many minerals look similar to calcite, and it also comes in so many aesthetics. Thus, visual inspection isn’t enough to determine its existence in a rock.
TIP: Even if calcite is really soft mineral it can be tumbled. But you need to be careful because of its softness. Check out the complete guide in the article below:
Can You Tumble Calcite? Be Careful and Follow These Tips!
How to Identify Real Calcite?
Everyone’s favorite way of identifying calcite is the acid test. It is described in every article about calcite. But the obstacle is obvious.
Does anybody have hydrochloric acid or HCl at home? Sure, it’s just next to the coffee and tea box. Let us help you to conduct all the necessary experiments with the stuff you have at home.
Real calcite has double refraction. It means when you try to see something through transparent real calcite, you’ll see it doubled. Also, an acid test will help you to identify real calcite. Put a drop of week hydrochloric acid or HCl and you’ll see a quick reaction – the formation of gas bubbles.
To identify real calcite, you need to conduct two experiments:
- Optical. To see the double refraction of real calcite in case you have a transparent crystal.
- Acid test. It works on any form and any color of real calcite.
Double refraction is an optical phenomenon when light passes through calcite and splits into two rays. Take a book or a newspaper, then place the calcite mineral on top of the printed word. In the case of real calcite, you will see how printed words split into two. If it does not, then it is fake calcite.
Hydrochloric acid (HCl) is suggested to be the best to conduct this experiment. However, it’s obvious that usually, people don’t have it at home.
We suggest using vinegar instead of hydrochloric acid. The reaction will not be so active, but the vinegar alternative is safer for kids.
When you place a drop of a weak acid, such as vinegar, on calcite, it will bubble. This happens because a reaction causes a little bit of the calcite to break down, releasing carbon dioxide gas, making bubbles.
This reaction is stated by the formula:
CaCO3 + 2HCl = CaCl2 (calcium chloride) + H2O (water) + CO2 (carbon dioxide)
The rapid release of carbon dioxide gas creates bubbles of effervescence. Mineral-effervescence tests are usually performed with cold, dilute hydrochloric acid. Effervescence is apparent when just a single drop of this acid contacts a calcite surface.
Bonus UV test!
If you have a blacklight at home (UV lamp for nails will also work), put your calcite under UV light. Real calcite glows under UV in red, blue, white, pink, green, and orange colors.
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):
- Smithsonian Handbooks: Rocks & Minerals
- Gemstone & Crystal Properties (Quick Study Home)
- Ultimate Explorer Field Guide: Rocks and Minerals (National Geographic Kids)
How to Spot Fake Calcite?
Fake calcite can be represented by a bunch of natural minerals, which look similar to natural calcite. They are quartz, halite, gypsum, selenite, dolomite, celestine.
Fake calcite will occur in any crystal form except rhombohedra and scalenohedra. Fake calcite will not react with acid. The hardness of fake calcite in most cases is high and fake calcite cannot be scratched by a knife or a window glass. Also, fake calcite usually doesn’t glow under UV light.
Fake calcite can be spotted the next way:
- It doesn’t react with dilute hydrochloric acid without
- It doesn’t fluoresce under UV light,
- Single fake crystal doesn’t exhibit birefringence (‘double refraction’).
TIP: The forming process of rocks and minerals indicates a lot of their characteristics. Do you know how long different types of rocks form? Find out the answer in the article below:
How Long Do Rocks Form? Answers For ALL Types of Rocks
Real vs. Fake Calcite The Main Differences
The main difference between real and fake calcite is that the real one occurs in the rhombohedral form of crystal, has double refraction, and reacts with hydrochloric acid with the formation of gas bubbles. Fake calcites are usually harder than real ones and cannot be scratched by a knife.
Here is a helpful table for you to easily compare the main features of fake and real calcite.
|Characteristic property||Real calcite||Fake calcite|
|Crystal form||Rhododendron. No right angles.||Cubic, prism, pyramids. Right angles are present.|
|Cleavage||Perfect in three directions.||Hase no cleavage. Have good cleavage in only one direction.|
|Double refraction||Clearly visible in transparent crystals||No double refraction at all.|
|Reaction with HCl acid||Active reaction with weak acids.||No reaction. Some carbonates in powdered form can react with warm HCl acid.|
|Hardness||Soft mineral (3 on the Mohs scale). Can be scratched by a copper pin, steel knife, and window glass.||In most cases are harder. Cannot be scratched by a copper pin.|
|UV light||Brightly glow under UV light in orange-red colors mostly.||Usually inert to UV light|
Real calcite has a lot of unique features that can help to distinguish it from fakes easily. Calcite fakes are usually other natural minerals, which look similar to calcite.
The most common imitations are represented by quartz, halite, gypsum, selenite, dolomite, and celestine.
Here are the characteristics that will help you to differentiate real calcite from fakes:
- Crystal form. Real calcite occurs in the form of rhombohedra and scalenohedra and has no right angles.
- Cleavage. Real calcite has perfect cleavage in three directions.
- Double refraction. Objects will seem doubled when viewed through transparent crystals of calcite.
- Reaction with acid. Real calcite actively reacts with weak acids like HCl and vinegar.
- Hardness. Real calcite is a soft mineral and can be scratched by a copper needle.
Glow under UV light. Real calcite mostly glows vivid orange-red color under UV light.
TIP: The real calcite is one of the minerals that glow under UV light. Do you know what other minerals glow under UV light? Check them out in the article below: