Have ever struggled to tell the difference between selenite and calcite?
They are both mineral forms, and here is a comparison between the two.
Selenite vs Calcite: Explained
What Is Selenite?
Selenite in its common form clear is a gypsum crystal.
Selenite is known by different names.
Some of the common names include desert rose, satin spar, and gypsum flower.
Although they share a common name, the appearances of each selenite type are different.
In mineralogy, selenite has “crystal habit” characteristics that are variant.
If selenite does not have a clear appearance, then other minerals are present.
This is what causes other varieties to naturally occur, such as desert rose for example.
The “crystal habit” of selenite (the external shape of the individual crystal or agate of crystals), is naturally transparent compared to its counterparts in the same family.
Also, this sulfate mineral most commonly has prismatic, columnar, or tubular-shaped crystals.
However, selenite can have a variety of habits that have not inclusions or imperfections.
Swallowtail twins or twinned crystals are the most common.
Interestingly, the Santa Sabina in Rome, Italy has windowpanes that have were with use selenite crystals.
This unusual fact is acknowledged for a good reason.
That is because the formation of the selenite used for construction purposes (i.e., windowpanes) are naturally formed thin sheets, reminiscent of mica.
One of the amazing things that selenite can do is attach itself to other base rocks or groundmass (matrix).
Whole selenite can be discovered floating freely in clay beds as well.
It is imperative to know that although selenite is a gypsum crystal, gypsum itself can occur on a variety of sulfate minerals.
Gypsum is the most widespread of all known sulfate minerals, and for this reason, it can be easy to misinterpret the appearance of selenite as something else.
Gypsum crystals are pallid.
This means that if there are in any impurities present in selenite gypsum crystals, other colors will be visible.
Minerals found in clay and iron oxides in selenite can cause vibrant blue, red, and yellow colors to name a few.
What Is Calcite?
Calcite is a carbonate mineral that can originate from aragonite within a span of days or a lesser time.
The right temperature for this natural occurrence to happen is 572 °F.
A lesser-known fact is that calcite is a mineral that is rock-forming.
Calcite was used in the construction of the United States Supreme Court building, and for tremendous justification.
Calcite is found in the two popular rocks that are used in construction.
The famous rocks are commonly marble and limestone.
Calcite can be found in many more forms, including other sedimentary and metamorphic rocks.
Did you know that calcite is used as an acid neutralizer? (For scientific reference only.)
It is used in over-the-counter and prescribed antacid tablets.
This carbonate mineral has over eight hundred identified types.
The habit of the mineral includes prism, scalenohedral, tabular, and rhombohedral forms.
The appearance of calcite can be found to have a semi-clear structure to a grain-stone appearance.
Dependent on other impurities and minerals that are involved in the natural formation of calcite, colors can range from dark grey, orange tint, red tint, pink, and white to name a few.
It is easy to mistake calcite for dolomite when examined under a microscope.
Interestingly, calcite can be mistaken as selenite.
Similarities Between Selenite and Calcite
Calcite and selenite have a few similarities.
They are both softer minerals and are easy to scratch.
Each of the crystals can have various colors dependent on the minerals that cause impurities.
Selenite can be found in prism form, and so can selenite.
There is evidence of both crystals being in clear form.
Both minerals are used in the construction industry.
Differences Between Calcite and Selenite
There are many differences between selenite and calcite.
Selenite is in the gypsum family of minerals and has a Mohs hardness of about two.
Calcite can be found existing in other rocks and has a Mohs hardness score of about three.
Furthermore, the chemical makeup of calcite is CaCO3, and it has an absolute hardness of fourteen.
Whereas selenite has a chemical make of CaSO4 – 2 H2O and has an absolute hardness score of 2 (the same number as the Mohs score).
More than likely, you will find selenite as a standalone crystal that is not formed inside of another rock-like calcite.
As aforementioned, calcite can be found in other rock forms such as marble and limestone.
Why do People Confuse Selenite as Calcite?
There are many reasons why people confuse these two crystals.
Many people confuse two because both can appear clear in nature.
Also, when they are in impurities, they can take on different colors, making it even harder to distinguish the two.
Many people do not realize that calcite is found in other mesomorph and sedimentary rocks.
More than likely, you have not found selenite if smaller-sized crystals are in another rock.
For example, when you look in a piece of granite or marble, you may notice some shiny flecks.
The shiny flecks are more than likely calcite.
Because of the way calcite is naturally formed in nature, you did more than likely found it in another rock than in standalone form such as selenite.
Also, the origins of each crystal and where they were found can give you clues into whether it is selenite or calcite.
If your specimen was found around marble or granite, it is more likely it is not selenite.
Each specimen is developed in different natural situations.
Selenite, a sulfate mineral, is in the Gypsum family and gypsum is evaporative (think about natural alabaster).
While you might frequently find calcite on the edges of creeks, streams, and lakes, it is rare to find selenite in water, as it dissolves.
Typically, people get them mixed up because of the white tones or clearness of the crystals.
A sufficient way to tell if you have a specimen that is selenite is to know that calcite is a harder specimen and usually always is found in metamorphic and sedimentary rock.
For example, calcite principally is formed with the essences of marine organisms, plankton, shells, and red algae to name a few.
Calcite can be found in caves in New Mexico USA.
Whereas, selenite can be found in the ancient plains of Oklahoma USA (Great Salt Plains Lake bed).