Sunday, May 12, 2013


1863, Western Theater: Union General Ulysses S. Grant advances toward the Mississippi  capital of Jackson during his bold and daring drive to take Vicksburg, the last Confederate stronghold on the Mississippi River. In April, Grant, however, had to contend with two Rebel forces. John C. Pemberton had an army defending Vicksburg, and Joseph Johnston was mustering troops in Jackson, 40 miles east of Vicksburg. Grant's advance placed him between the two Southern commands. He planned to strike Johnston in Jackson, defeat him, and then focus on Vicksburg when the threat to his rear was eliminated. On May 12, Grant's troops encountered a Rebel force at Raymond, Mississippi, which they easily defeated. (

Most books that I read for enjoyment are works of non-fiction.  For example, I have enjoyed keeping up on the sesquicentennial remembrances  of the American Civil War/War Between the States.  Events of 150 years ago are coming alive for me.  But, at times I indulge in fiction where the authors seem to have an interesting vision and knowledge of the great outdoors, especially the American Southwest and/or Rocky Mountains.  Tony Hillerman was a master at describing the landscapes of  northern Arizona and New Mexico--actual localities.  Louis L'amour had a number of imaginary localities but his geological descriptions were superb--I am a big fan of the wandering Sackett clan.  And now, I have embarked on the adventures of the Cochise County, Arizona, Sheriff, Joanna Brady, created by J. A. Jance.
A particular paragraph written by L'amour intrigued me for several years.    He was describing, in the novel Galloway, the trials of Flagan Sackett, alone and in the wilderness, trying to start a fire to broil elk meat that he nabbed from a wolf: What I hunted was iron pyrites, and I found several chunks and broke off two pieces to use in starting a fire…I tried striking the two chunks of iron pyrite together.  The sparks came easy, but it taken nearly an hour to get one into the shredded leaves and the bark.  I always wondered, was this fire-starting feat possible?

Scattered pyrite crystals in a sedimentary limestone.  Width of specimen ~12 cm.
 Iron pyrite, sometimes termed Fool’s Gold, is really the mineral pyrite and is an iron disulfide with a chemical formula FeS2 (about 47% iron and 53% sulfur).  It often appears in nature as cubes with striations (fine parallel lines) on the cube faces.  Collectors also may observe octahedral or pyritohedron crystals.  The brass yellow color is quite distinctive and pyrite has a hardness of about 6 to 6.5.  The luster is metallic and the specific gravity is around 5.  The mineral is also brittle and breaks quite easily into small pieces or powder.  When rubbed on a streak plate the mineral smells like sulfur and leaves an almost black streak. Unlike gold, pyrite is not malleable (flexible and pliable) and hence the story that miners gave a shiny specimen the “bite test” to determine if it was gold!  The name pyrite comes from the Greek and means fire.  Perhaps that is a clue to answering my question.
Nice cubes of pyrite from Eagle Mine at Gilman, Colorado.  Width of specimen ~3 cm.
Pyrite is perhaps the most common sulfide mineral and is found in all groups of rocks from sedimentary to igneous to metamorphic.  The mineral marcasite has the same chemical formula as pyrite (a polymorph) but whereas pyrite is in the isometric crystal system, marcasite is orthorhombic.  Sometimes the two minerals are difficult to distinguish from each other; however, marcasite is “lighter in weight” with a density of about 4.8 and seems more brittle.  Interestingly, marcasite jewelry seen at the trade shows is actually made of pyrite!

Cluster of marcasite crystals, with scattered calcite, from la Sirena Mine, Guanajuato, Mexico.  Width of specimen ~10 cm.   
Pyrite is a very collectable mineral and some of the specimens are quite spectacular and sell for many dollars.  On the other hand, it is possible to purchase small crystals for a very reasonable price and is a great way to get youngsters hooked on collecting minerals.  In Colorado one may collect small crystals “by the dozen” at some of the mine dumps near Leadville and the CSMS Pebble Pups/Juniors have experienced some fantastic field trips to the area.

One of the more interesting occurrences of pyrite and/or marcasite is the relative uncommon action when either becomes the replacing mineral in the process of fossilization.  This series of changes takes place in stagnant solutions or waters with poor circulation and where large amounts of hydrogen sulfide are created, often by decaying animal or plant matter.  The sulfide then combines with iron in the sediment to form FeS2 and begins to replace the original shell material.  Some of the more spectacular pyritized fossils are the Devonian brachiopods (Mucrospirifer) from the Midwest.

On the other hand. paleontologists, but especially vertebrate paleontologists and museum workers are often concerned about “pyrite disease” eating up their specimens.  If fossil “bones” (as an example) contain even small amounts of pyrite and are exposed to conditions of high humidity then the mineral begins to oxidize and forms iron sulfate (perhaps the mineral melanterite), FeSO4.  Iron sulfate is of greater volume that iron sulfide (pyrite) and so causes expansion in the specimens and breakage and crumbling soon follow.  In addition, sulfuric acid forms and discolors the specimens.  Once pyrite disease begins the process seems irreversible.  That is one reason museum collections are stored in dry conditions, 45% humidity or less.  And, individual collectors should keep their prized fossil specimens in a sealed container along with a package of silica gel, a desiccant.  Without proper storage they may begin to oxidize within a few months.  Larger specimens of pyrite cubes are slower to oxidize and most collectors will only see some “tarnishing” on their specimens.  This is the same chemical reaction, plus water and perhaps microbes, that produces the very acidic (sulfuric acid) acid mine drainage.

Another interesting occurrence of pyrite is the discoidal concretions plucked from coal mines in Illinois (and perhaps elsewhere) that are aptly named “pyrite suns” or “pyrite dollars”.   Early collectors believed them to be fossil sand dollars (a type of echinoderm); however, they probably represent pyrite crystals that did not have room to grow into cubes.

So, can you start a fire with pyrite?  I found references to using flint (microcrystalline quartz) and fine-grained pyrite as fire starting tools.  The outdoorsman should bang the two minerals together so that small pieces of pyrite “fall off” as sparks.  The secret seems to be getting the sparks to ignite---you need very dry and fine tinder.  In my experiments I could produce the sparks but could not get the ignition--UNTIL I changed the tinder to lint from the electric clothes dryer (is this cheating?).  Perhaps the sparks were too cool for "normal" grass tinder!  On the other hand, there is a great video of a person flailing away at a piece of pyrite with a fragment of flint until the tinder ignites: 

I also know that pieces of pyrite were used in Wheelock guns during the 1500’s and 1600's.  The pyrite was put into a clamp (a dog in gunsmithing parlance) and when released struck a piece of hardened steel. The sparks produced from this action then ignited the priming pan that in turn ignited the main powder charge.   If this sounds cumbersome realize the Wheelock replaced the Matchlock where “shooters” needed to put a lighted match to the priming pan!  Talk about delayed reactions--waiting for the recoil!

There also seems to be some evidence that “nature” uses pyrite to start fires in coal beds and in “oil shales”.   Scientists know that oxidation of pyrite is an exothermic process (a chemical reaction where heat is produced) and if the oxidation occurs in a closed environment (as in a waste pile) the dissipation of heat is inefficient and the temperatures rises (Schoonen and others, 2000).  What this means--heat is produced when pyrite is exposed to oxygen in a somewhat closed system.

With this knowledge in mind, the 10 December 2008 issue of the New Scientist ( reported on a wildfire in 2004 near Santa Barbara, California, that researchers traced to a recent landslide but were uncertain about how the fire started.   Geologists from the US Geological Survey visited the site and found that the temperature of the rocks in the landslide was 307 ° C - hot enough to start a fire. They determined that a chemical reaction in the rocks caused the ignition.  Furthermore they noted the landslide exposed pyrite to the air, which in turn caused an oxidation reaction that heated a nearby patch of low-grade coal to more than 300 ° C!

Downriver (Missouri River) from Chamberlain, South Dakota, at a place termed Burning Brule, low grade "oil shale" beds of the Sharon Springs Member of the Pierre Shale (Cretaceous) actually "burned", or at least smouldered for several years.  In the winter months the heat produced was quite noticeable as a rising plume in the otherwise cold air.  I presume the "fire" was caused by a lightening strike. As a bit of trivia--Burning Brule was later the site of a "nightclub" where adult beverages flowed freely.  The boat trip back to Chamberlain, in the darkened night, often was exciting!

In 1804 members of the Lewis and Clark expedition looked nearby for the existence of a volcano!  It seems that the explorers were told to watch out for volcanoes as they passed through this region:  On September 14, 1804 both captains walked on Shore with a view to find an old Volcano Said to be in this neighborhood by Mr. McKey [a gentleman from St. Charles, MO].  Could not see any Signs of a Volcanoe.  Earlier in the expedition (August 24, 1804) Clark had noted in his diary while passing through Nebraska: West under rugged Bluffs 1¾ ms. passing Several Small Dreens [drains], falling into the river those Bluffs has been lately on fire and is yet verry Hott, Great appearance of Coal, & imence quantities of Cabalt in Side of that part of the Bluff which Sliped in (Moulton, 1986)

Early settlers in this part of northeastern Nebraska were fearful of this erupting volcano (the “Ionia Volcano”, Clark’s burning bluff) until the early 1900’s when geologists proved that the burning was started by the oxidation heat created by damp pyritiferous and carbonaceous Carlile Shale (Cretaceous and older than the Pierre) on fresh exposures provided by the rapid erosion of the river bluffs (Moulton, 1986).

As for Flagan Sackett starting the fire to broil elk meat--pyrite has a long history of being used in the fire starting process.  Today, campers and hikers today often carry magnesium sticks and a steel striker (as well as phosphous matches).  But, if you get in trouble, look for those pieces of pyrite and some chert!


Moulton, G. E., (ED), 1986, The Journals of the Lewis and Clark Expedition: Lincoln, University of Nebraska Press.

Schoonen, M., A. Elsetinow, M. Borda, and D. Strongin, 2000, Effect of Temperature on Pyrite Oxidation Between pH 2 and 6: Geochemical Transactions 2000, article 4, online journal: