Marcasite

Authors: Taylor, Ittzel, and Vanessa

Mineral Name: Marcasite

Chemical Composition: Marcasite has a chemical composition of Iron Sulfide, FeS2 . (1)

Color: Marcasite comes in a few different colors Including but not limited to yellow to silvery in color, yellow, or yellow-bronze. (1) After time the mineral changes to a brownish color over time when stored inside. (1)

Streak: Dark grey to black. (1)

Hardness: The hardness is 6-6.5 on the Moh’s hardness scale. (1) That can cut a steel nail.

Cleavage/Fracture: Marcasite has conchoidal-type fracture and has cleavage of 2 plains, though they can be hard to see. Conchoidal fracture looks very similar to a shell with a smooth and curved surface. This can also been seen in a broken glass. (8).

Crystal Form: The crystal system for marcasite is orthorhombic. (2) The crystal shapes that marcasite forms are a bi-pyramidal shape, with the bases of the crystal in a pyramid shape connected by long vertical lines. Marcasite can also be tabular in shape showing a thin form that has 4 sides. It can also form in the shape of an aggregate coxcomb, which are tubular crystals that form together at the base and create slender arc-like crystals. (2) They can also come in many different forms as well such as a massive with no defining shape or radiating slender crystals connected together at a central point. (1) Encrusting is another formation of marcasite that makes a crust over another rock or mineral. Lastly, marcasite can form radiating disks that look like sand dollars. (2)

Luster: Marcasite has a metallic luster when it shows a fresh surface, but it has a submetallic luster when it has been tarnished. (1).

Special Features: If marcasite is left alone for a long period of time it will oxidize. While it oxidizes it won’t change color but it will eventually produce sulfuric acid that will disintegrate anything holding the mineral. Once fully oxidized it will become dust particles. An easy way to distinguish between marcasite and pyrite is the sulfur-smell it has while oxidizing. (7)

Varieties: The most closest associated variety with marcasite would be Blueite, which is the nickel-bearing variety of marcasite. (4) Lonchidite is an arsenic-bearing variety of marcasite (4)

Mineral Group: Marcasite is in the simple sulfides group and this is because it has a chemical composition that includes sulfide S2. (2).

Environment: Marcasite is actually formed in 3 different ways. Marcasite can form from very acidic water on Earth’s surface or in near-surface environments. (1) Usually this mineral is formed in highly acidic, low temperature conditions. Marcasite can also be formed in sedimentary environments. For instance, marcasite can form in coal deposits during diagenesis, which is when sediments transform into sedimentary rock. (1) The organic material that is necessary for coal formation produces a weakly acidic environment that forms sulfide minerals. Marcasite can also form in clays and limestones, especially when fossils composed of organic materials are present creating an acidic environment like coal. Marcasite is one sulfide mineral out of many sulfide minerals to be deposited in hydrothermal deposits in veins along fractures in rocks. (1)

Associated Minerals and Rock types: There are many minerals that are associated with marcasite, especially pyrite but also pyrrhotite, galena, sphalerite, fluorite, dolomite, or calcite. (1) Associated rock types include the metamorphic/metasomatic rock boetonite as well as iron-ore and iron sulfide-ore. (4)

Occurrence in North America: If you are looking for Marcasite in North America you can find the mineral on both the East and West coasts. Specific states include Maine, Rhode Island, Pennsylvania, Virgina, North Carolina, and Florida, which are the major areas on the East coast where you can find marcasite. (5) Lastly on the West coast, marcasite locations would include Washington, Nevada, and Oregon down to California. Not all mines are open to the public, but many states can produce this mineral, in proper conditions. (5)

Economic Uses: Marcasite has a huge impact economically when it is found within coal. Marcasite contributes to the emissions of sulfur dioxide during the combustion of coal. Typically, the majority of coal seams consist of a very little amount of marcasite; but in other cases, Marcasite is the main sulfide mineral and the main source of sulfur within coal. (1). Burning high-sulfur coal can cause acid rain, which can create expensive problems locally. Another economic use of marcasite is in jewelry. It was more common to wear marcasite jewelry in the late 1800's and early 1900’s as “Victorian and Art Nouveau designs”. (1) However, most marcasite jewelry is not actually made of marcasite because the mineral is too brittle and chemically unstable, eventually breaking down into powder. (1) Marcasite can even weather to other sulfate minerals that become corrosive when exposed to moisture or humidity. (1)

Industrial Uses: Marcasite was used mostly during the Industrial Revolution to create sulfuric acid by extracting sulfuric gases from the mineral through a process called roasting. Roasting is when marcasite (or pyrite) has heat added till it begins to give off sulfuric gases. These gases are extracted and dissolved in water to make sulfuric acid. Currently, marcasite is used to make sulfuric acid to be used in fertilizer production. (7)

First Notable Identification: Walter Pope first talked about finding marcasite in 1665 in the mercury ores of the Idria Mine, Cividale del Friuli in the Julian Alps of Slovenia. (4) He mentioned how the mercury ore had gold spots in it, but after testing the spots they were found not to be gold but what is now known as marcasite and pyrite (4). Later, in 1845, Wilhelm Karl von Haidinger gave the mineral the name “Marcasite”. It is unclear of who first discovered marcasite, but the word is Arabic or Moorish. (4) The name was linked to pyrite and other similar metallic minerals that had that bronze tone. (4)

How We Identified It: Marcasite looks very similar to pyrite due to its luster, but is way more brittle.

Don’t Confuse It With: Marcasite is often confused with pyrite (fool’s gold). (1) Although they both come from the same chemical compounds, the only way you are able to tell them apart is the fact that pyrites crystals are commonly cubed and marcasites crystals are commonly in the shape of a needle or a blade. Marcasite is also more brittle. (1) The streak is also another way you can tell the difference between the two. Pyrite has a greenish streak, while marcasite has a greyish streak. (1). Overall pyrite is the closest mineral associated with marcasite in terms of chemical formula and in the way it looks. However, they are not the same in regard to several properties, which make each one uniquely different.



Bibliography:

  1. King, Hobart M. (2019). Marcasite Mineral Properties and Uses, Geo-science News and Information, geology.com/minerals/marcasite.shtml. Accessed 6 June 2019.

  2. The Mineral Marcasite, edited by Hershel Friedman, The Mineral and Gemstone Kingdom, www.minerals.net/mineral/marcasite.aspx. Accessed 6 June 2019.

  3. “Pyrite and Marcasite.” Illinois State Geological Survey, isgs.illinois.edu/pyrite-and-marcasite.

  4. Kucera, M. (2019). Marcasite: Mineral information, data and localities.. [online] Mindat.org. Available at: https://www.mindat.org/min-2571.html [Accessed 7 Jun. 2019].

  5. Jewelrynotes.com. (2019). Places Where You Can Find Marcasite. [online] Available at: https://www.jewelrynotes.com/where-to-find-marcasite-locations/ [Accessed 7 Jun. 2019].

  6. Galleries.com. (2019). MARCASITE (Iron Sulfide). [online] Available at: http://www.galleries.com/Marcasite [Accessed 7 Jun. 2019]

  7. Rickard, D. (2019). The Many Faces of Fool's Gold. [online] American Scientist. Available at: https://www.americanscientist.org/article/the-many-faces-of-fools-gold [Accessed 7 Jun. 2019].