by Ken Rock, MSDC Editor
This question got my attention on a recent edition of Jeopardy. The reference to fool's gold that won't finance anyone's retirement is an attempt to help the players get the right answer – which someone did before I came up with mine.
It turns out that my response, disulfide, was NOT the answer Jeopardy was looking for. The correct Jeopardy response, in the form of a question, was "what is pyrite" (also known as iron disulfide, or FeS2). I was aware that flint was somehow used in a firing mechanism to generate a spark, but was not aware that pyrite had also been used to generate sparks.
The first self-igniting firearm action used a wheellock mechanism that depended on two elements:
(1) a spring-activated, serrated wheel that revolves when the trigger is pulled, and
(2) a piece of pyrite held in jaws that force it against the wheel.
When the wheel was spun against the pyrite, sparks were generated that ignited a small amount of gunpowder in the priming pan. The resultant “flash in the pan” was transferred through a small hole to the propulsion charge in the barrel, causing the gun to fire. A close modern analogy of the wheellock mechanism is the operation of a handheld lighter (e.g., "BIC") where a toothed steel wheel is spun in contact with a piece of sparking material to ignite the liquid or gaseous fuel.
Research shows that Neanderthals were able to start fires using stone tools. The findings, published in the journal Scientific Reports, present the first evidence (based on actual stone artifacts) of systematic fire production by our extinct close relatives.
Evidence from the Middle Paleolithic, which spans 300,000 to 50,000 years ago, shows that Neanderthals regularly used fire. However, it was unclear whether they collected natural fire or produced it themselves. There also is ample evidence suggesting that humans used pyrite to strike flint. Indeed, flint tools that likely were used for this purpose have been found at numerous Homo sapiens archaeological sites throughout Eurasia.
The familiar fire-starting method of producing a shower of sparks over tinder by striking steel against flint originated much later in time, during the Iron Age (~1200 BC to 600 BC) that followed the Stone Age and Bronze Age. However, no dedicated fire-making tools have been found at Neanderthal sites. Any flint tools that have been found appear to have been used for other things, such as animal butchering.
Later Uses of Pyrite
Pyrite was important in the production of sulfur and sulfuric acid, especially during the World War II era. Long before this use though, pyrite was valued by some Native American peoples as a healing stone. During the Victorian Age, pyrite was a favorite stone for creating carved rosettes, shoe buckles, rings and other decorative elements.
Pyrite is the most common sulfide mineral and forms in many geologic environments, all over the world, and many pyrite deposits also contain small amounts of other minerals such as cobalt, nickel, silver and gold. Pyrite crystallography is particularly fascinating, with crystals forming nearly perfect cubes, octahedrons, pyritohedrons (12-sided crystals with pentagon-shaped faces), and a variety of crystal shapes that are combinations of those forms. In fact, pyrite has its own display case in the Geology, Gems & Mineral Hall of the Smithsonian's Natural History Museum that focuses on its varied shapes.
Pyrite crystals sometime exhibit a form known as penetration twinning, where two or more crystals are intergrown. A classic locality for pyrite penetration twins is the remarkable deposit at La Rioja, Navajún, Spain.
The Incredible Pyrite of Navajún, Spain
Most mineral collectors can remember first looking at a pyrite from Navajún and thinking: “No way are those cubes natural.” But we can rest assured that those beautiful cubic crystals are most definitely natural and can be found in several locations near Navajún, Spain.
I can recall seeing a room full of these amazing pyrites at the Tucson Gem & Mineral Show many years ago and being stunned by the beauty and variety of the specimens, almost all of which featured those lovely cubic crystals. I remain convinced that Navajún has got to be one of the most remarkable mineral occurrences known.
The host rock is marl, dating to the Cretaceous Period (from ~145 to 66 million years ago). At the Victoria Mine there are three major zones where inclined Cretaceous marl containing the pyrite crystals outcrop at surface. The thickness of each of these strata varies, but averages about 8 feet. The average inclination of the formation is approximately 15%.
For more about an amazing site visit to the pyrite mines of Navajún by Raymond McDougall, owner of McDougall Minerals, click HERE. Raymond was kind enough to allow use of information and photos from his wonderfully detailed trip report which includes information about the nearby towns, pyrite mineralogy, and current specimen mining operations.
Pyrite from the Victoria Mine is often mirror-bright, sharp and perfect beyond compare. Although pyrite is too abundant and wonderfully varied to proclaim the “world’s best pyrite,” these are generally regarded as the world’s best cubic crystals of pyrite. Crystals range in size from 1mm up to, rarely, about 20 cm. As is true throughout the world of minerals, the larger crystals typically are not as brilliantly lustrous and razor sharp as the smaller ones – although stunning, jaw-dropping large crystals have been found here.
Although what we tend to see in museums, mineral shows, and photographs are typically the perfect sharp cubes with mirror luster, in fact the mode of occurrence and condition of Victoria Mine pyrites varies considerably. Some of the pyrite crystals can be quite distorted, and some show varying degrees of oxidation. Although most of the crystal forms found at the Victoria Mine (and at other nearby localities in this region) are cubic, pyritohedral (12 sided) crystals are also present at the locality. Cuboctahedral crystals (combination of square and triangular faces) also have been found, but are rare at the Victoria Mine.
The pyrite crystals occur encased within a very thin soft coating. This coating protects the crystals and is likely one of the reasons we are able to enjoy such wonderfully preserved crystals, but on the other hand, it leads the crystals to want to detach from the matrix!
The matrix itself is incredibly weak and friable, and water causes it to deteriorate – the only thing this stuff wants to do is crumble. (Important Note: NEVER clean a matrix pyrite specimen from Navajún in water – it will fall apart!)
Because of the friable matrix, many joints between interlocking pyrite crystals have weakened, so that when you collect them, they most often detach and roll out of the rock as individual single crystals with points of contact where they were formerly attached to or interlocked with others. This is not always the case with tight groups or, for example, closely interlocked pairs, but overall it is incredibly common.
When the Final Jeopardy Category is "Best of the Best"
As you can probably tell, pyrite is one of my favorite minerals and the pyrites of Navajún are especially near and dear to my heart. Be sure to check out these remarkable specimens in person on your next visit to the Smithsonian. And when the Final Jeopardy answer is revealed stating “This location in Europe produces the best cubic pyrite specimens in the world,” be ready with the question “What is La Rioja, Navajún, Spain.”