If elements were rated by their popular image, sulfur wouldn’t have a chance. Just the mention of the word conjures unsettling thoughts of noxious volcanic gases, acrid smoke, odors of decaying organic matter and even the fundamentalist Christian “fire-and-brimstone” concept.
But, image problems aside, sulfur has a lot going for it. Widely collected for its beautiful, bright-yellow crystals, sulfur has been a staple in medicine for 4,000 years. Under its old name “brimstone,” it appears frequently in both the Bible and alchemical texts. Today, sulfur is a major industrial commodity with myriad uses. In contradiction of a fundamental tenet of mineral-resource supply and demand, sulfur use has reached record highs, yet sulfur mining has virtually ceased.
Sulfur Mineral Properties and Occurrence
Elemental sulfur most often crystallizes in the orthorhombic system; two rare sulfur polymorphs crystallize in the monoclinic system. Sulfur crystals are brittle and have a resinous luster. Depending upon the presence of impurities, they range from transparent to opaque. Colors range from bright, dandelion yellow and greenish-yellow to subdued grays and browns. Elemental sulfur has a Mohs hardness of 1.5 to 2.5. It has a low specific gravity of 2.07 and a very low melting point of 226°F.
Sulfur is abundant in Earth’s crust. Most is chemically bonded into sulfate and sulfide minerals, organic and biomass materials, coal and petroleum. Minerals containing sulfur include pyrite (iron disulfide), galena (lead sulfide), chalcopyrite (copper iron sulfide), sphalerite (zinc sulfide) and gypsum (calcium sulfate). Relatively little sulfur exists in its native state.
Elemental sulfur occurs in evaporite concentrations in sedimentary rocks and as earthy and encrusting forms at certain hot springs, fumaroles and volcanic vents. It also forms massive deposits within the limestone caprock that overlies many underground salt domes.
Fumigants and Gunpowder
The Chinese were using sulfur medicinally by 2000 B.C. Sulfur-based ointments were used to alleviate skin ailments. Burning sulfur generated sulfur dioxide gas that cleared nasal passages and fumigated insect-infested materials and dwellings.
The Chinese initially obtained limited amounts of sulfur from volcanic fumaroles. By the time these sources were depleted around 300 B.C., they had learned to heat pyrite in kilns and condense the resulting “golden vapors” into elemental sulfur. By the first century C.E., other Asian and European cultures were also heating pyrite to obtain sulfur.
The Chinese also pioneered the science and craft of pyrotechnics. They used crude black powder, a combustible, slow-burning mixture of potassium nitrate (saltpeter) and powdered coal. Around 800 C.E., they invented gunpowder by adding sulfur to crude black powder to lower its ignition temperature and increase combustion speed. When contained and ignited, gunpowder exploded violently, an attribute of enormous military and historical consequence. By the 1400s, sulfur had become an important component of gunpowder, one of its earliest major uses.
Brimstone and the Philosopher’s Stone
Because native sulfur melts into a syrupy, red liquid that burns with an eerie blue flame, it caught the attention of many ancient cultures. In the Bible, sulfur is associated with judgment, destruction and divine wrath. Most familiar is the Genesis account of the Lord raining down “fire and brimstone” upon the wicked cities of Sodom and Gomorrah.
Medieval alchemists were particularly interested in sulfur. The German philosopher and alchemist Paracelsus (Philippus von Hohenheim) listed sulfur, mercury and salt as the three alchemical principles. Sulfur represented heat and transformation, growth and change, and the soul’s journey toward enlightenment and self-discovery. Many alchemists believed that sulfur itself was the long-sought-after philosopher’s stone that could transmute common metals into gold.
Alchemy also had its practical benefits. In the ninth century C.E., the Arabic alchemist Jabir ibn Hayyan was credited with producing sulfuric acid from elemental sulfur. Although difficult and costly to make, sulfuric acid, with its ability to dissolve many metals and materials, was a gift to alchemy. It was an invaluable tool for investigating the composition of materials. The experimental use of sulfuric acid paved the way toward the later emergence of analytical chemistry.
Sicily: The World’s Great Sulfur Source
The world’s first great source of sulfur was Italy’s island of Sicily. The ancient Greeks began mining it from outcrops around 200 B.C. Sicily remained a source of sulfur for centuries. During the 19th century, its vast evaporite deposits supplied most of the world’s sulfur.
When traditional, costly and time-consuming methods of obtaining sulfur from pyrite proved unable to meet demand, attention shifted to the development of Sicily’s extensive underground deposits. By 1810, Sicily was producing three-quarters of the world’s sulfur, while pyrite mining had almost ceased.
Sulfur mining in Sicily reached its peak in 1900, with 700 small, underground mines turning out a half-million tonnes of high-grade sulfur ore. Although vital to the Sicilian economy, these mines comprised a dark chapter in mining history. Most were accessed by decline tunnels with hundreds of steps hewn into the rock. Among Sicily’s thousands of sulfur miners were children as young as 12.
Conditions were horrific in the poorly ventilated underground workings. There, temperatures exceeded 100°F, humidity was high, and the air was laced with hydrogen sulfide gas. Cave-ins were common in the unstable workings; during the 1800s, an estimated 2,000 miners lost their lives.
After visiting Sicily during a European tour in 1910, the African-American educator, author and former slave Booker T. Washington wrote: “. . . a sulfur mine in Sicily is about the nearest thing to hell that I expect to see in this life.”
Sulphurdale, Utah
During the late 19th century, the United States began obtaining sulfur from aptly named Sulphurdale, Utah. There, bubbling hot springs formed crusts and layers of sulfur. Disregarding the foul-smelling hydrogen sulfide gas that emanated continuously from the springs, Mormon settlers harvested the sulfur to make gunpowder.
Sulphurdale rests atop heavily faulted bedrock near a dormant volcano. A shallow magmatic body underlying this volcano forced superheated water rich in dissolved hydrogen sulfide upward into shallow beds of porous volcanic tuff, where the water cooled to precipitate elemental sulfur in massive and disseminated forms.
In 1883, mine developer Ferdinand Dickert built a small, thermal-extraction furnace to melt the impure sulfur in an oxygen-deficient environment to yield pure, molten sulfur. Dickert was soon shipping 1,000 tonnes of sulfur per year. By 1890, the company town of Sulphurdale, with 30 homes, a general store and a school, had become the nation’s leading domestic source of sulfur.
Frasch Mining
In the late 19th century, oil-well drillers in Louisiana and Texas discovered subterranean pools of petroleum associated with salt domes. These are geologic formations where salt and sulfur had risen upward to concentrate beneath strata of impervious limestone. These domes contained huge amounts of native sulfur with great potential value—if it could be extracted economically.
In 1894, German-born American chemical engineer Hermann Frasch developed a process for drilling wells into these subterranean deposits and injecting superheated water to melt the sulfur. Subsequent injection of compressed air forced the liquid sulfur into extraction wells for transport to the surface.
Frasch mining greatly increased the supply of sulfur while slashing production costs, just in time to meet soaring demand driven by a boom in sulfuric-acid manufacturing. By 1900, the massive salt domes of Louisiana and Texas had become the world’s leading source of sulfur. Frasch mining also triggered the steady decline of sulfur mining in Sicily and forced the abandonment of Sulphurdale, Utah.
Frasch mining dominated global sulfur production for decades until it, too, became a victim of technological progress. In the early 1970s, environmental restrictions in the United States and Europe required the reduction of huge quantities of sulfur-laden gases from metal smelters, coal-fired power plants, petroleum refineries and natural-gas processing plants.
To meet these new standards, researchers developed technologies to strip sulfur from liquid and gas fuels before use and to scrub sulfur from smokestack emissions. The vast tonnages of cheap sulfur recovered from fuel processing and smokestack scrubbers quickly made Frasch mining uneconomical.
Sulfur Today
Today, most recovered sulfur comes from petroleum refining, natural-gas processing and other industrial operations rather than conventional mining. Conventional mining and the last remaining Frasch operation account for only a small fraction of global sulfur production.
The United States has no remaining elemental sulfur mines or Frasch operations. Yet, thanks to sulfur recovered during fuel processing and smokestack scrubbing, it is self-sufficient in sulfur and remains one of the world’s leading producers.
China is also a major sulfur producer. Historically, much of its sulfur came from roasting pyrite, a heavily polluting practice that has largely been displaced in many parts of the world by sulfur recovery from industrial processes.
Annual global sulfur production has reached roughly 70 million tonnes. About 90 percent of recovered sulfur is made into sulfuric acid, by far the most widely used inorganic chemical. Sulfuric acid is essential to numerous industrial processes, including the manufacture of fertilizers.
With the decline of conventional sulfur mining, industrial recovery has transformed the sulfur industry. Sulfur use remains high, but the source of most of the world’s supply has changed dramatically.
Sulfur Specimens
With its sharp-edged, translucent-to-transparent, bipyramidal and tabular crystals, elemental sulfur is a widely collected mineral. Unlike many minerals associated with volcanic environments, pure elemental sulfur does not have an odor. Its color—a pure yellow so intense that it seems to glow—is what really catches the eye.
Historically, the finest sulfur specimens—large plates of well-developed, brightly colored, gemmy crystals—have come from Sicily, where the long-inactive mines still yield occasional specimens. Fine specimens have also come from other localities, including Russia, Spain and Bolivia.
With the closing of Sicily’s mines and the decline of conventional sulfur mining elsewhere, crystalline sulfur specimens have become increasingly scarce. It is possible that the finest specimens have already been collected.
Despite its maligned image, sulfur betters our lives every day. In one form or another, it is contained in, or used to make, pharmaceuticals, tires, agricultural fertilizers, paper, auto batteries, food preservatives and many other products—even our kitchen matches that produce the familiar, acrid “sulfur” smoke.
The “Blue Lava” of Kawah Ijen
Among the few small-scale volcanic sources still yielding sulfur today is the Kawah Ijen volcano on the Indonesian island of Java. Inside its steaming, 9,000-foot-high crater, artisanal miners dig sulfur encrustations that accumulate from condensed volcanic gases. These miners channel the continuously venting, sulfur-rich gases through ceramic pipes, where they condense into a liquid that solidifies into massive sulfur.
This sulfur is then broken into pieces and loaded into baskets that are manually carried from the crater floor 900 vertical feet upward to the rim, then two miles down the mountain to a small sulfur refinery. Miners can earn $15 per day, making two round-trips—a strenuous journey made more difficult by breathing air laced with hydrogen sulfide and sulfur dioxide gases. A workforce of 200 miners recovers about 14 tonnes of sulfur per day.
Kawah Ijen is also notable for its “blue lava”—eerie, nighttime displays of blue flames created as venting sulfur-laden gases ignite in the presence of atmospheric oxygen. These vivid, 15-foot-high, electric-blue flames are invisible during the day but spectacular at night.
In 2023, the United Nations Educational, Scientific and Cultural Organization (UNESCO) added Kawah Ijen to its Global Geoparks Network as an important part of Earth’s geological heritage. Tourism has since increased, with the main attraction being guided, midnight hiking tours—a two-hour hike up the volcano rim followed by a 45-minute descent into the crater—to witness and photograph the striking blue flames.
This story about sulphur was written for Rock & Gem magazine. Click here to subscribe. Story by Steve Voynick.
