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Pyrite
by Brian Meinhardt
Physical Geology
Fall 2007
         

A Pyrite's Life For Me                                                 

      

 

Credit photo: John Zander

 

The mineral pyrite, also known as iron pyrite (or the more saddening name to many a miner “fools gold”) is a useful and, in my opinion, particularly enjoyable mineral to observe. The word pyrite comes from the Greek word pyr, meaning “fire”, and is named so because it emits sparks when struck by steel. Pyrite can be found all over the world, but in the United States it is most abundant in Illinois and Missouri. Pictured is a great representation of what you can expect to see in a pyrite crystal structure.
 

Pyrite is in the class of minerals called sulfides and is one of the most abundant minerals in its class. Pyrite is a brassy-gold color with a metallic luster, and its streak is a greenish-black. The hardness of pyrite, according to Mohs Scale of Hardness ranges from a 6 to a 6.5. Pyrite crystals are most often found in the form of a cube (as opposed to marcasite which is Orthorhombic). The picture I have illustrated shows the schematic representation (feS2=iron sulfide) where blue=iron and yellow=sulfur that belongs to pyrite.
 

 

Euhedral parabolic pyrite crystals

Credit photo: Brian Meinhardt             Credit photo: www.wikipedia.com

 

 

Believe it or not, the mineral pyrite does not start out as pyrite. Pyrite originates from the mineral marcasite.  These two minerals are almost identical in appearance, and have the same chemistry. However, they have different symmetry and crystal shapes, which makes pyrite a pseudomorph of marcasite. The main difference between the two minerals, in terms of usability, is that marcasite can crumble and pyrite is stable.

 

Pyrite has several economical uses. Personally, I have found only three that are of any substantial use at present day, as well as one possible (and not so efficient) use if the future demands it.  First, the possible future use of pyrite would be the commercial need of iron ore. If and when, other, more concentrated minerals rich in iron ore are depleted, pyrite may be the answer. However, because pyrite is not an efficient or significant source of iron ore, it is not being used as of today.
 

The next use of pyrite commercially, is in jewelry (in some cases, very elegant and classical jewelry). In fact, pyrites use in jewelry is not a new idea or practice. The first recorded use of pyrite in jewelry was during the reign of Louis XIV of France between the years of 1643 and 1715 to make distinguished belt buckles and brooches. Today, when pyrite is used in jewelry it is often referenced under its trade name as “marcasite”, which is similar, as was mentioned earlier, but is not the exact same mineral. I believe the use of this trade name is due to the idea that “marcasite” sounds more valuable than “pyrite” or “fools gold”.
 

 

Credit photos: www.ebay.com
 

 

The third mentionable use for pyrite is creating sulfur dioxide. Sulfur dioxide kills yeasts, molds, and bacteria, and is also used in preserving dried fruits while allowing them to retain their original color. Sulfur dioxide is also an important chemical in the paper making process. When you combine sulfur dioxide with water and oxygen it naturally produces the next commercial use of pyrite, which is the production of sulfuric acid.
 

 Sulfuric acid has large commercial value due to its highly corrosive properties. However, newer, more efficient methods of harvesting sulfuric acid with different materials have reduced the use of pyrite for this process, due to pyrite being just a minor ore for the acid. One down side to pyrites ease of conversion to sulfuric acid (in small amounts), is that it can occur naturally. When being mined, for example, pyrite can be exposed to the elements and sulfuric acid is naturally created. In a mine, this is called acid mine drainage. As with all drainage of water, it will reach streams and/or rivers, usually turning them a milky-red, which is due to the iron content in sulfides like pyrite. This occurrence is devastating to rivers and all aquatic life within those rivers. Also, it contaminates the water, making it unfit for human consumption.
 

 

 

            Earlier I discussed how pyrite is a pseudomorph of marcasite. I have found that, just as pyrite began its life as marcasite, it does not always end its life as pyrite. Just over a week ago, I was hiking in the Huachuca Mountains and found several very small dark brown cubes approx. 2-5 mm in width. The largest was in bad shape and could no longer be called a cube, but the second largest had a width of 1cm and was a perfect, undisrupted cube. After a long period of research I narrowed it down to pyrite or galena.  Both have square crystals, with the major difference being that galena is a lead ore and pyrite is an iron ore. I brought the specimens into my physical geology class where my teacher, Roger Weller, with no hesitation identified it as limonite, pseudomorphed from pyrite. Basically, what has happened is that hydrated iron oxide minerals replace the pyrite, and it is then called limonite. Which obviously declares that limonite is not actually a mineral, but a grouping of minerals. When I discovered that this cube originated as pyrite I was particularly excited, since pyrite is the topic of this report. Pictured are photographs taken of the cubes I found in the Huachuca’s. From the photos you can see their sizes, as well as their particularly high metallic luster (a characteristic passed on from the pyrite).
 


 

Credit photos: Brian Meinhardt

 

Credit photo: Brian Meinhardt
 

 

            In conclusion, pyrite is a useful and beautiful mineral, like so many other minerals on our planet, and it was a pleasure sharing it with you.

Credit photo: www.wikipedia.com

 

 

Works Cited

 

1.) http://reviews.ebay.com/What-is-Marcasite_W0QQugidZ10000000001408894

2.) http://en.wikipedia.org/wiki/Pyrite  photo released under the GNU Free Documentation    License.

3.) http://mineral.galleries.com/minerals/sulfides/pyrite/pyrite.htm   Jon Zander GFDL and CC-by-SA-2.5. See Below

 

4.) skywalker.cochise.edu/.../pyrite/pyriteL.htm R. Weller/Cochise College

 

5.) http://www.britannica.com/search?query=pyrite&ct=

 

6.) www.appalachian-center.org/.../water/index.html

 

7.) www.galleries.com/.../limonite/limonite.htm