Found a whitish-looking rock?
Could be calcite. Or something else.
In this article, we’ll give you some tips to learn how to identify it.
How To Identify Calcite (EXPLAINED)
Introduction To Calcite
Calcite is a carbonate mineral that forms in many different colors.
Most popular calcite minerals are clear or white, but there are also blue and pink crystals as well.
Some common calcite crystals have rhombohedral shapes with straight edges and corners, although some species form hexagonal prisms that can be six-sided or twelve-sided.
The color the mineral displays is dependent on both its environment and its purity.
Impurities can absorb some of the light passing through them.
In its pure state, calcite is a carbonate mineral that can be found in many different colors and shapes.
The color of the mineral depends largely on its purity and environment.
Calcite crystals can come in clear or white forms, while some species are blue or pink as well.
Some common calcite minerals have six-sided rhombohedral shapes with straight edges and corners, while other types form hexagonal prisms that may be twelve-sided.
Quartz is an impurity that absorbs light when present in the crystal structure of calcite, giving it a cloudy appearance.
You can identify calcite by its pink, blue, or white color and its rhombohedral form.
Additionally, the mineral is a carbonate with a Moh’s hardness of 3 to 4 and a specific gravity of 2.72.
Look at its color
Calcite has many different colors, but it’s most commonly found in clear and white forms.
Although some specimens can also be blue or pink, the purest crystals are clear and colorless.
The cloudy quartz content sometimes present in calcite can give it a very light color, but even in these cases, the stone is usually white or clear.
Look at its shape
Calcite comes in many different shapes, including hexagonal prisms with six-sided symmetry and rhombohedral crystals with straight edges and corners.
However, it’s important to note that not all calcite minerals have these shapes.
Determine its symmetry
Determine whether calcite has rhombohedral or hexagonal symmetry.
If the mineral has six-sided symmetry, you should be sure to look at it closely, because while some forms of calcite do display this shape, others come in twelve-sided prisms.
Study its optical properties under magnification
Calcite has weak double refraction, meaning that it usually appears as two separate images when viewed through the stone.
This effect is noticeable even to the unaided eye in some specimens and may be present only under magnification.
Perform tests for hardness and specific gravity
Measure the specimen’s hardness with a mineral identification kit and its specific gravity with a scale.
While calcite has a Moh’s hardness of 3 to 4, quartz is much harder at 7.
Examine the specimen’s fluorescence under ultraviolet light
Most specimens do not fluoresce, but some calcite can glow a creamy white color when viewed under blacklight.
Look closely at the cleavage and luster of the specimen
Calcite has perfect cleavage on rhombohedral faces and good cleavage on prism and basal faces.
It also exhibits vitreous to pearly luster, although this property may be less obvious in some specimens.
Observe its surroundings
The mineral commonly forms in sedimentary and metamorphic rocks that contain limestone or dolomite.
It may also be found in some hydrothermal veins.
Calcite is commonly found in places such as Mexico, Oklahoma, Morocco, and Ohio.
Calcite can be commonly confused with quartz, another form of silica with a different chemical composition.
Calcite has weak double refraction, while quartz does not display this property.
Another difference between the two minerals is that calcite has perfect cleavage on rhombohedral faces and good cleavage on prism and basal faces, while quartz displays no cleavage at all.
Quartz also commonly occurs as hexagonal prisms with six-sided symmetry, while calcite only rarely displays this pattern.
Additionally, quartz has a Mohs hardness of 7 and a specific gravity of 2.65 to 2.75 while calcite has a Moh’s hardness of 3 to 4 and a specific gravity of 2.72 to 2.82.
Quartz is commonly found in countries such as Switzerland, the United States, Mexico, and other places.
Additionally, it is easier to test for because almost all quartz specimens have hexagonal symmetry.
Calcite mineral specimens are most commonly found in clear and white forms, although some also occur in blue or pink.
The purest crystals are colorless, but cloudy quartz content sometimes present in calcite can give it a very light color, although even these stones are usually still clear or white.
It’s important to note that not all calcite is clear or white.
While these specimens are most common, the mineral also occurs in many colors, such as blue, pink, green, yellow, and more.
The most popular colored varieties of calcite include blue Mexican (or Aztec) onyx and rose onyx.
In order to identify calcite, you should begin by considering its physical properties.
Calcite has rhombohedral or hexagonal symmetry, weak double refraction, perfect cleavage on rhombohedral faces, and good cleavage on prism and basal faces, vitreous to pearly luster, can fluoresce under ultraviolet light, commonly found with limestone or dolomite, and forms in sedimentary or metamorphic rocks.
Additionally, it’s important to consider the surroundings of your specimen because calcite is commonly found in places such as Mexico, Oklahoma, Morocco, and Ohio.
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