Chalcopyrite

Authors: Deidre, Esme, and Stephanie

Mineral Name: Chalcopyrite

Chemical Composition: (CuFeS2) Copper Iron Sulfide

Color: Brass-yellow, dull gray-green, acid treated tarnish red-blue-purple iridescence

Streak: Chalcopyrite has a greenish gray/black streak.

Hardness: 3.5-4 on the Moh’s hardness scale.

Cleavage/Fracture: Chalcopyrite has poor cleavage, which means it does not have clearly defined cleavage. Instead it has very uneven fracture. This means that when chalcopyrite is under stress is does not break in a smooth or even plane; in contrast, it will break in choppy, irregular surfaces.

Crystal Form: Chalcopyrite's crystalline form is classified in the tetragonal crystal system, meaning that it has four sides that each form in a triangular shape. Its crystals can also be an octahedron, massive (no clear form), or grainy. The most unique looking form chalcopyrite can take is reniform, which will appear as small rounded bulges lumped together. (19)

Luster: Chalcopyrite has a metallic luster although, it loses its metallic luster with weathering.

Special Features: When chalcopyrite tarnishes in acid it shines a red, blue and purple iridescence. When weathered chalcopyrite also loses its metallic brassy yellow color. (12)

Varieties: There are many varieties of chalcopyrite. Auriferous Chalcopyrite has microscopic bits of gold that are embedded in the mineral while Stannian Chalcopyrite is a form of chalcopyrite that contains tin. One of the more unusual varieties is Blister Copper, which forms in round sections resembling grapes, or blisters, that are lumped together (10). Peacock Ore is a more commonly known variety because of its vibrant colors and resemblance to a peacock’s coloring. Other varieties include zinc-rich Zincian Chalcopyrite, platinum group elements-rich Chalcopyrite and Argentina Chalcopyrite. (2)

Mineral Group: Chalcopyrite is a sulfide. A sulfide means that it is a mineral where sulphur and metallic elements, such as iron, copper or tin, have combined (3 & 9).

Environment: Chalcopyrite can be found in almost all of the Earth’s sulfide deposits. These locations are often medium to high temperature hydrothermal veins. These veins are located in igneous and/or metamorphic rocks (6). Chalcopyrite can form in several different ways including within crystallization melts of igneous rocks, contact metamorphism, hydrothermal metamorphism, and in pegmatite dykes (12).

Associated Rock types: Associated rocks of chalcopyrite will be certain igneous or metamorphic rocks. Igneous rocks form from the cooling of magma or lava, while metamorphic rock form through the application of heat and pressure (17). Some specific rocks that are associated with chalcopyrite include schist, gneiss, and granite. These rocks may contain minerals that are commonly associated with chalcopyrite such as quartz, azurite, baryte, brochantite, calcite, dolomite, malachite, pyrite, sphalerite, galena and other minerals. (2, 4 & 12)

Occurrence in North America: You can find chalcopyrite in Canada, Northern Wisconsin and Northern Minnesota, the Sonora Desert in Arizona, New Mexico, and California. Mining also occurs in Mexico just south of the US border and Baja California. Other locations include Oklahoma, Missouri, Colorado, New York, New Jersey and Pennsylvania. (5 & 7)

Economic Uses: Chalcopyrite is polished into cheap jewelry such as pendants and beads (12). For instance, chalcopyrite can be formed into cabochons, which are smooth and rounded on one side and flat on the other. Cabochons are typically cheap because they are glued or attached with adhesive wax which may not last as long as other jewelry (11).

Industrial Uses: Chalcopyrite is mainly used for the copper that it contains. The most important use for chalcopyrite is as an ore of copper. Chalcopyrite does not yield as much copper as other copper-rich rocks; however, it is more abundant and widespread making it the most accessible copper source. Copper is a vital material in our everyday lives. During ancient times, copper was used to make bronze and brass. At times it was even used for healing (18). Now copper is used as a conductor of heat and electricity that is used to heat homes, give light and even transport water to us. The copper is extracted from copper ore by a 7 step process. First, the ore (chalcopyrite in this case) is crushed. Second, a solution is added to the powered rock that makes the copper water repellant and the solution frothy. Air is then pushed up through the mixture which creates bubbles that trap the copper inside. The bubbly froth at the top of the solution is then scraped off and the excess material is discarded. Third, the froth, now containing the copper, is then roasted between 500 °C and 700 °C to change the copper from an impure mineral to a pure metal (8). With chalcopyrite, the iron and sulfur are removed during this roasting process. The resulting product is called calcine. Fourth, the calcine is heated to 1200 °C and silica and limestone are added (8). This causes a reaction that allows for impurities to float to the surface and be removed. What is left at the end is called matte (8). Matte is a combination of copper sulfides and iron sulfides. Fifth, iron is eliminated from the matte by oxidation, leaving behind what is called blister copper (8). Sixth, the blister copper is poured into anodes that allow for it to be cooled in sheets (8). At this point in the extracting and refining process the copper is nearly pure. However to truly purify it, it must endure the seventh step; electrolytic refining (8). This process removes the remaining impurities by submerging the blister copper in an electrolyte that has copper sulfate and sulfuric acid (8). Once immersed, a low voltage current is sent through the solution and the impurities will settle to the bottom of the solution. Now you have pure, refined copper (8).

First Notable Identification: Chalcopyrite was named in 1725 by Johann Friedrich Hinckel (2). This name is derived from the Greek word “chalkos” which translates to copper, and “pyrites” which means to “strike fire”. (2)

How It Is Identified: Chalcopyrite is a brittle mineral that appears brassy or gold in coloring. The streak of chalcopyrite is a greenish gray and it is soft enough that it can be scratched by a nail (12).

Don’t Confuse It With: Most often Chalcopyrite is confused with Gold, Pyrite or Bornite. Chalcopyrite can be easily confused with gold and pyrite but what helps to identify these economic minerals the fact that gold for one does not tarnish and has a yellow streak. Chalcopyrite does tarnish giving a blue, red and purple iridescence and has a greenish-gray/black streak. With pyrite, the best way to tell these two minerals apart is by testing its hardness. Pyrite has a hardness of 6.5 and chalcopyrite has a hardness of 3.5-4. While Bornite has a similar streak, you can tell the difference because it is softer and tarnishes more easily then chalcopyrite (13, 14 & 15).



Bibliography:

  1. Barthelmy, Dave. Mineral Tenacity and Fracture, www.webmineral.com/help/Fracture.shtml#.XMtjEI5Kjcs.

  2. Chalcopyrite.” Chalcopyrite: Mineral Information, Data and Localities., www.mindat.org/min-955.html.

  3. “Chalcopyrite.” Geology - Rocks and Minerals, flexiblelearning.auckland.ac.nz/rocks_minerals/minerals/chalcopyrite.html.

  4. “Chalcopyrite.” Geology Science, 11 Apr. 2019, geologyscience.com/minerals/chalcopyrite/.

  5. “Chalcopyrite from Sonoran Desert, North America.” Mindat.org, www.mindat.org/locentries.php?p=289404&m=955.

  6. “Chalcopyrite- Sulfides.” Esci.umn.edu, University of Minnesota, www.esci.umn.edu/courses/1001/minerals/chalcopyrite.shtml.

  7. “Chalcopyrite: The Mineral Chalcopyrite Information and Pictures.” Minerals.net, Hershel Friedman, www.minerals.net/mineral/chalcopyrite.aspx.

  8. “Copper Mining and Extraction Sulfide Ores.” Copper Development Institution, European Copper Institute, copperalliance.org.uk/knowledge-base/education/education-resources/copper-mining-extraction-sulfide-ores/.

  9. “Glossary.” Geology - Rocks and Minerals, flexiblelearning.auckland.ac.nz/rocks_minerals/glossary.html#s.

  10. “Glossary of Terms- Botryoidal.” Minerals.net, www.minerals.net/mineral_glossary/botryoidal.aspx.

  11. “How Are Gems Cut and Polished?” Nature.berkeley.edu, nature.berkeley.edu/classes/eps2/wisc/teleport/howcut.html.

  12. King, Hobart M. “Chalcopyrite.” Geology.com, geology.com/minerals/chalcopyrite.shtml.

  13. King, Hobart M. “Fool's Gold.” Geology.com, geology.com/gold/fools-gold/.

  14. King, Hobart M. “Bornite.” Geology.com, geology.com/minerals/bornite.shtml.

  15. Madhusha. “Difference Between Pyrite and Chalcopyrite.” Pediaa.Com, 23 Nov. 2017, pediaa.com/difference-between-pyrite-and-chalcopyrite/.

  16. “Mineral ID Chart.” Napavalley.edu, www.napavalley.edu/people/rmcarthur/Documents/Lab Resources/Mineral ID Charts.pdf.

  17. Msn. “Rock Cycle - Rocks .” Msnucleus.org, msnucleus.org/membership/html/k-6/rc/rocks/3/rcr3_1a.html.

  18. Oakes, Liz. “Chalcopyrite...A Mystery Stone Connecting You To Higher Realms.” HealingCrystalsForYou.com, www.healing-crystals-for-you.com/chalcopyrite.html.

  19. “Tetrahedron.” Merriam-Webster, Merriam-Webster, www.merriam-webster.com/dictionary/tetrahedron.