When was calcite discovered

There are several varieties of calcite and it would be impossible to describe them all. However there are a few standouts. Possibly the most well known of calcite's varieties is its most common form, the classic scalenohedron or " Dogtooth Spar " as it is sometimes called. This variety appears as a double pyramid or dipyramid , but is actually a distinctly different form. The point of the scalenohedron is sharp and resembles the canine tooth of a dog, hence the name.

Beautiful clear colorless or amber-orange examples of this variety are considered classics and outstanding examples come from Pugh Quarry, Ohio; Cornwall , England and Elmwood, Tennessee but the variety is found worldwide. Not necessarily a variety of calcite, cave formations are certainly a unique aspect of calcite's story.

Calcite is the primary mineral component in cave formations. Stalactites and stalagmites, cave veils, cave pearls, "soda straws" and the many other different cave formations that millions of visitors to underground caverns enjoy are made of calcite. It is the fact that calcite is readily dissolved that these formations occur.

Overlying limestones or marbles are dissolved away by years and years of slightly acidic ground water to percolate into the caverns below. In fact the caverns themselves may have been the result of water dissolving away the calcite rich rock.

As the calcite enriched water enters a relatively dry cavern, the water starts to evaporate and thus precipitate the calcite. The resulting accumulations of calcite are generally extremely pure and are colored if at all, by very small amounts of iron or other impurities. Mexican onyx is a variety of calcite that is used extensively for ornamental purposes.

It is carved into figurines and is so popular that almost every child in the USA owns a small onyx animal or two. Carvings such as vases, bookends, plates, eggs, obilisks, pyramids and statues are all popular. It is not the same onyx as the quartz variety of onyx which is a little more precious it is used in jewelry and is banded white and black. To avoid confusion it is best to refer to it as Mexican Onyx.

Mexican onyx is banded with multiple orange, yellow, red, tan, brown and white colors that have marble-like texture. The carvings are quite attractive and affordable; a rare combination! Another variety is the so called " Iceland Spar ", which is basically clear cleaved fragments of completely colorless ice-like calcite.

Originally discovered and named after Eskifjord, Iceland where the calcite is found in basalt cavities. In rock shops around the world, iceland spar is available in large quantities and at affordable prices and are popular among children. Most of today's iceland spar comes from Mexico. The iceland spar displays the classic cleavage form of calcite, the rhombohedron. Iceland spar was and is used for optical equipment and during World War II it was a strategic mineral as it was used for the sighting equipment of bombardiers and gunners.

It is iceland spar that best demonstrates the unique property of calcite called double refraction. Double refraction occurs when a ray of light enters the crystal and due to calcite's unique optical properties, the ray is split into fast and slow beams. As these two beams exit the crystal they are bent into two different angles known as angles of refraction because the angle is affected by the speed of the beams. A person viewing into the crystal will see two images The best way to view the double refraction is by placing the crystal on a straight line or printed word the result will be two lines or two words.

There is only one direction that the beams are both the same speed and that is parallel to the C-axis or primary trigonal axis. Rotation of the crystal will reveal the direction in the crystal that is parallel to the C-axis when the line or word becomes whole again. By contrast, the direction perpendicular to the C-axis will have the greatest separation. The extremely high index of refraction of calcite that causes the easily seen double refraction is also responsible for the interference colors pastel rainbow colors that are seen in calcites that have small fractures.

Fluorescence , phosphorescence , thermoluminescence and triboluminescence are other important properties of calcite. Although not all specimens demonstrate these properties, some do quite well and this is diagnostic in some cases. One notable case of fluorescence occurs at Franklin, New Jersey where the massive calcite is enriched in a small amount of manganese and fluoresces a bright red under UV light. Some Mexican iceland spar can fluoresce a nice purple or blue color and unique specimens will even phosphoresce continue to glow after the UV source has been removed.

Triboluminescence is supposedly a property that should occur in most specimens, but is not easily demonstrated. It occurs when the specimen is struck or put under pressure; in a dark room the specimen should glow when this happens.

The best property of calcite is the acid test. Because calcite always will effervesce bubble when even cold weak acids are placed on specimens.

Even the cement in sandstones will effervesce assuring the geologist of identification of the cementing mineral. These materials are easily mixed, transported, and placed in the form of a slurry that will harden into a durable construction material. Concrete is used to make buildings, highways, bridges, walls, and many other structures.

Calcite with cleavage: Transparent calcite from Baxter Springs, Kansas, showing characteristic cleavage.

Specimen is approximately four inches 10 centimeters across. Calcite as agrilime: Acid-neutralizing qualities of calcite make finely crushed limestone a preferred material for soil treatment. Calcite as an antacid: The acid-neutralizing ability of calcite is used in medicine. High-purity calcite was used to make these antacid tablets. Calcite has numerous uses as a neutralizer of acids. For hundreds of years, limestones and marbles have been crushed and spread on fields as an acid-neutralizing soil treatment.

They are also heated to produce lime that has a much faster reaction rate in the soil. Calcite is used as an acid neutralizer in the chemical industry. In areas were streams are plagued with acid mine drainage, crushed limestone is dispensed into the streams to neutralize their waters. Calcium carbonate derived from high-purity limestones or marbles is used in medicine.

Mixed with sugar and flavoring, calcium carbonate is made into chewable tablets used in the neutralization of stomach acids. It is also an ingredient in numerous medications used to treat digestive and other ailments. Sorbents are substances that have the ability to "capture" another substance.

Limestone is often treated and used as sorbent material during the burning of fossil fuels. Calcium carbonate reacts with sulfur dioxide and other gases in the combustion emissions, absorbs them, and prevents them from escaping to the atmosphere. Calcite as marble blocks: White marble blocks for monuments or statuary, awaiting transport from a quarry in Portugal.

Marble is an attractive and easily worked rock that has long been used for monuments and sculptures. Its lack of significant porosity allows it to stand up well to freeze-thaw action outdoors, and its low hardness makes it an easy stone to work. It has been used in projects as large as the pyramids and as small as a figurine. It is widely used as cemetery markers, statues, mantles, benches, stairways, and much more.

Calcite as chalk: Calcite in the form of chalk from Dover, England. Specimen is about 4 inches 10 centimeters across. The best way to learn about minerals is to study with a collection of small specimens that you can handle, examine, and observe their properties. Inexpensive mineral collections are available in the Geology.

In a powdered form, calcite often has an extremely white color. Powdered calcite is often used as a white pigment or "whiting. It is a primary ingredient in whitewash, and it is used as an inert coloring ingredient of paint. Pulverized limestone and marble are often used as a dietary supplement in animal feed. Chickens that produce eggs and cattle that produce milk need to consume a calcium-rich diet.

Small amounts of calcium carbonate are often added to their feeds to enhance their calcium intake. Calcite has a hardness of three on the Mohs scale , and that makes it suitable as a low-hardness abrasive. It is softer than the stone, porcelain, and plastic surfaces found in kitchens and bathrooms but more durable than dried food and other debris that people want to remove. Its low hardness makes it an effective cleaning agent that does not damage the surface being cleaned.

Pulverized limestone is also used as a mine safety dust. This is a nonflammable dust that is sprayed onto the walls and roofs of underground coal mines to reduce the amount of coal dust in the air which can be an explosion hazard. The mine safety dust adheres to the wall of the mine and immobilizes the coal dust. Its white color aids in illumination of the mine.

It is the perfect material for this use. Carbon dioxide is an important gas in Earth's environment. In the atmosphere it serves as a greenhouse gas that works to trap and hold heat near the surface of the planet.

The process of limestone formation removes carbon dioxide from the atmosphere and stores it away for long periods of time.

This process has been occurring for millions of years - producing enormous volumes of stored carbon dioxide. When these rocks are weathered, used to neutralize acids, heated to make cement or metamorphosed severely, some of their carbon dioxide is released and returned to the atmosphere.

All of these processes of limestone formation and destruction have an impact on Earth's climate. Calcite as lithographic limestone: Calcite in the form of lithographic limestone from Solnhofen, Bavaria, Germany. Note the fine, uniform texture that is characteristic of lithographic limestone. Specimen is about 4 inches ten centimeters across. Calcite as oolitic limestone: Calcite in the form of oolitic limestone from Tyrone, Pennsylvania.

Calcite as translucent onyx: Calcite in the form of translucent onyx from Tecali, Mexico. This specimen shows excellent double refraction. Calcite as calcareous tufa: Calcite in the form of calcareous tufa from Mumford, New York. Calcite as travertine: Calcite in the form of travertine from Tivoli, Italy.