New Mexico Mineral Symposium — Abstracts

David Rickard’s recent book Pyrite: A natural history of fool’s gold (Oxford University Press, 2015) has given us an enthusiastic recasting of pyrite, not as common-as-dirt fool’s gold and metaphor for false values, but as a “super-hero” mineral that influenced human evolution and culture, science and industry, and ancient, modern and future Earth environments.

In a style as effusive as Carl Sagan’s in his Cosmos, Rickard’s paean to pyrite serves to reawaken interest in a mineral so often taken for granted. Commonplace they may be yet pyrite crystals work a siren call that lures us in despite our best efforts to resist. This bright, shiny mineral enthralls people of all ages, cultures and backgrounds. Budding collectors gravitate to pyrite right out of the gate thanks to its allure, abundance and affordability; it’s our gateway “drug.” Therefore, revisiting an old, comfortable friend of the mineral world, and refreshing what we know of its history and nature, is a worthwhile pursuit.

The Usual Basics
Name: pyrite (early – py-ri-tes, iron pyrites) from the Greek pyr for “fire” because it sparks when struck with stone or iron, and, hence, a useful fire starter.
The metallic sulfide FeS2 occurs in virtually all geologic formations: sedimentary deposits, hydrothermal veins and metamorphic settings; and is commonly massive, granular, radiating, reniform, discoid, globular and crystalline in the isometric system – usually in cubes, irregular pentagonal dodecahedrons called “pyritohedrons,” octahedrons and rarely diploids. Pyrite displays a great variety of crystal forms for a common mineral. It and calcite go head to head in Goldschmidt’s Atlas of crystal drawings for the most sketches. The intriguing grooves in the faces of many pyrite crystals are the result of changing conditions that cause a crystal to change back and forth many times between a pyritohedron and a cube. Very rarely, in low-temperature, hydrothermal veins, pyrite will form minute, threadlike (filiform) crystals with right angle bends or coils. A “screw dislocation mechanism” is suggested for this phenomenon (Henderson and Francis 1969).

With its pale, brassy-yellow color and metallic luster, pyrite bears a close enough resemblance to gold to dupe the gullible and early on earned the label “fool’s gold.” It further helped spawn the familiar phrase “All that glitters is not gold.” Shakespeare uses it verbatim in The Merchant of Venice. The phrase was considered proverbial by the 16th century.

Of course, in reality, pyrite’s physical characteristics are far from gold-like. Pyrite fails the density test with gold—5 grams/cm3 to 19 grams/cm3. Pyrite is twice as hard as gold; its color is off; and it certainly is not malleable with its conchoidal fracture and brittle tenacity.

Historical and Modern Uses
Pyrite has proved to be a utilitarian mineral for mankind, serving him in many an imaginative way, increasing in sophistication as he developed his arsenal of scientific tools. Probably the earliest application of pyrite was as a fire-starter. No smart, early human would go anywhere without his kit of pyrite and tinder. Striking rocks were everywhere.

A logical adaptation of the “pyrite makes sparks” technology to the human tendency to apply benign processes to the tools of war is seen in the evolution of firearms. In the 1500s the clumsy matchlock firearm gave way to the “wheel lock” mechanism. In simple terms, a piece of pyrite was levered against a spinning, grooved wheel that shot sparks into a pan of powder that, in turn, touched off the main charge. Finally, a weapon that could be concealed under clothing. This leap forward in firearm design led to the first gun control laws. Fear of assassination among the nobles of the day led to the wheel lock being banned throughout the Holy Roman Empire. Fortunately for the nobles, the wheel lock was too expensive to manufacture in any practical numbers. In no time at all, the flintlock replaced the wheel lock—so much for gun control.

Pyrite was used in classical times to produce copperas (iron sulfate). Pyrite was heaped and allowed to weather (an early leaching process). The acidic runoff was boiled with iron to produce the sulfate, a chemical used in the textile industry as a mordant, a dye fixative, and as a means to blacken leather, and also as ink.

By the 15th century, such leaching replaced the burning of pyrite as a step in the production of sulfuric acid, one of the most versatile chemicals ever discovered. While today much of elemental sulfur is produced as a byproduct of gas and oil production, Rickard claims some 14 million tons of pyrite are mined per year for its sulfur (85% in China); 7 million tons of sulfur (Rickard p. 47) are used in, what else, sulfuric acid production.

Pyrite has even served human vanity. Pre-Columbian Indians crafted mirrors of polished mosaic surfaces of pyrite. Queen Victoria and the Art Nouveau movement popularized “marcasite” (actually pyrite) jewelry. That such jewelry is still popular in our time serves as a bridge from the old to the new.

• Pyrite was used as a semi-conductor by crystal radio hobbyists.
• Pyrite has become a significant ore of gold thanks to the high price of gold.
• Combined with other conductors, it is used as cathode material in non-rechargeable batteries.
• It has been suggested as an abundant material to use in photovoltaic solar panels.
• Scientific applications abound, for example: Study of sedimentary pyrite may serve to probe ancient marine environments. Analysis of pyrite grains has added to our knowledge of early earth, especially the Great Oxygenation Event.
• New Age practitioners claim that pyrite is a protective, shielding stone to use as an amulet to deflect harm and danger; especially helpful when one is away from home or performing hazardous work.

Lastly, this presentation must visit the best known locations for collectible pyrite: Peru; Spain; the Island of Elba; Park City, Utah; Leadville, Gilpin, Rico, Central City, Colorado; Montana, King Co., WA and so on. Surely, someone’s favorite location will have been forgotten.