The mineral fluorite is very popular with collectors. Fluorite is a mineral that has a lot of color, and it’s often large. Fluorite also has another advantage. Fluorite’s history is just as fascinating as the mineralogy.
A Smelting Flux
Fluorite’s association with silver and lead ores first brought it to the attention of Roman miners. It was found to improve the smelting by reducing melting temperature and combining with impurities, resulting in a slag that could be easily removed.
German smelter workers in the 1500s used Fluorite (then known as Flusse) as a smelting fluid. In his classic “De Re Metallica,” German scholar Agricola (Georg Bauer) detailed the use of Flusspat, which he called “lapides igni liquiscentres.” This translates to “stones that become liquid in fire.” Agricola also referred to the mineral as Fluere from the Latin fluor meaning “to flow.” This is the origin of our modern word, fluorite.
A German glassworker thought that glass was impervious to liquids, until 1670. He mixed sulfuric acid and ground Flusspat in a container of glass. The glassworker was amazed when the glass dissolved. The glass-dissolving agent was a secondary acid that became known as Flusspatäure, literally “acid of Flusspat.”
The ability of Flusspatäure to etch glass brought new creativity to the art of glassmaking. More importantly, it indicated to chemists that both Flusspat and Flusspatäure contained an active, unknown element. Leading scientists aimed to identify and isolate this element for the rest of the century.
The “Fluorine martyrs”
This mysterious element was first named in 1813, although it had not yet been isolated. French physicist, André-Marie Ampère, acknowledged the element’s hazardous nature. He proposed the name “phtor,” which is the Greek word for “destructive.” English chemist Sir Humphry Davy adhered to tradition and coined the word “fluorine” from the old Latin fluor. In 1826, scientists adopted the words “fluoride” for fluorine-containing compounds and “hydrofluoric acid” for Flusspatäure.
Unfortunately, chemists have seriously underestimated fluorine’s dangers. More than 12 researchers have lost their health and lives after inhaling fluorine elemental or vapors containing fluorine. They became known as “fluorine martyrs.”
Frederick Henri Moissan was a French chemist who, in 1886, electrolytically reduced a mixture of hydrofluoric and potassium fluoride. He showed that the yellowish-orange gas was the element with the highest chemical activity. His work won him the Nobel Prize for Chemistry in 1906. Moissan, who was the last fluorine martyr, paid dearly for his honor. He died a year after receiving the award at the age of 55.
From the A-Bomb until the Present
During World War II, large amounts of fluorite were shipped from the Illinois-Kentucky District with fake bills of lading to nonexistent locations to confuse potential Axis spies. The fluorite’s true destination was a top-secret facility in Tennessee, where it was converted to elemental fluorine. The fluorite was converted into uranium gas hexafluoride for separation of fissionable isotope uranium-235 needed to create the atomic weapons that ended World War II.
It is a fluorite crystallized in an isometric system. It has a Mohs Hardness of 4.0 and a specific Gravity of 3.18. There are four directions of perfect cleavage. It is found in hydrothermal veins, and it is also a common component of sulfide ore of silver, lead and zinc.
Seven million metric tonnes of fluorspar are mined each year in the world. The half of the fluorspar is converted into hydrofluoric, an acid that can be used as a feedstock in many industrial chemical processes. The remainder is mainly used to melt steel and aluminium. China now produces half the world’s fluorspar; Mexico and South Africa are also important sources.
The fluorite that we collect is safe and stable because it contains calcium and fluorine ions. Fluorite should never be heated or treated with acids or other chemicals. Fluorite is more than what meets the eye, as the fluorine-martyrs tragically discovered.
This rock science column about fluorite minerals previously appeared in Rock & Gem magazine. Click here to subscribe. Story by Steve Voynick.
The post Fluorite Mineral Properties first appeared on Rock & Gem Magazine.