Fluorite – A Special Mineral of Many Forms and Colors
Fluorite is a unique mineral that forms in more colors than any other mineral on Earth. The most common colors are blue, red, purple, yellow, green, and white. In developing the Mohs Scale of Mineral Hardness, Friedrich Mohs chose fluorite as the example mineral for the hardness of four (4) on the scale.
Italian mineralogist Carlo Antonio Galeani Napione named the mineral in 1797. The name fluorite is derived from the Latin word “fluere” which means “to flow.” Fluorite was often used as a flux in iron smelting, which is believed to be the reason behind the name choice.
Fluorite often forms in low to high temperature hydrothermal veins inside rocks, especially those containing lead and zinc minerals. It is also present in some igneous and metamorphic rocks. Fluorite is often found with other minerals such as galena, calcite, quartz, sphalerite, and borite. Crystals of fluorite can form in cubes (squares) or octahedrons (diamond) shapes.
Common Properties of Fluorite
Formula: CaF2
Other Names: Fluorspar
Color: Blue, Red, Purple, Yellow, Pink, Champagne, Brown, Green, or White
Hardness: 4 on Mohs Hardness Scale
Streak: White
Luster: Glassy to Dull
Density: 3.175 – 3.56 g/cm3
Crystal Shape: Cubes, Octahedrons, Dodecahedrons. Sometimes twinned crystals occur.
Fracture: Conchoidal to splintery
Cleavage: Perfect Octahedral
Beautiful samples of fluorite exist in Germany, Italy, Switzerland, England, Mexico, Canada, and the United States. Fluorite is a common component in enamels, hydrofluoric acid, cooking utensils, telescopes, camera lenses, jewelry, and home décor items.
Fluorite Mineral Fun Facts
- Fluorite crystals often grow together which is called “twinning.”
- Fluorite crystals will fluoresce under ultraviolet light.
- Jewelers sometimes facet fluorite crystals and use them as imitation diamonds although it is a much softer mineral making fluorite less ideal as a gemstone.
- In addition to forming cubes and octahedrons, fluorite can occur in bands. One of the most famous forms of banded fluorite is called Blue John and found in Derbyshire, United Kingdom.
A Spectacular Rare Form of Fluorite
A rare type of striped, or banded, fluorite is the Blue John Fluorite found in the Blue John and Treak Cliff caverns in England. These caves are located in the Peak District in England near the town of Castleton, Derbyshire. The caverns formed within limestone strata that deposited in deep ocean waters millions of years ago. Layers of shale and some gritstone, a type of coarse sandstone common in this area, cover the limestone. The geology of the Blue John Cavern is fascinating and discussed further in a separate blog post.
This rare form of fluorite is so fascinating that it was the catalyst for an entire book series titled, the Crystal Cave Adventures. This book series starts when teenagers Emma and Brody fall through a time-traveling cave and land in 1775 England to steal a sample of the rare mineral for their friend, geologist Mr. M (aka Heath Matthews). Mr. M’s stunning rock and mineral collection is scheduled for national display when a thief breaks into his house and destroys all of his samples and maps. Emma and Brody vow to help rebuild the collection, later discovering the secret, magical time-traveling cave that Mr. M used to collect his unique samples. With one simple step, the adventure begins.
From the book, Blue John’s Cavern:
“The Blue John Fluorite is one of the rarest forms of a common mineral. Its name comes from the French words ‘Bleu Jaune’ which translates into English as ‘Blue-yellow.’ The Blue John form of the mineral is located in a hillside near a large mountain called Mam Tor, which is just outside of the town of Castleton,” Mr. M said. He stopped walking and opened a long tube he was carrying and removed a street map. Mrs. M, Emma, and Brody held the map open as he pointed to a solid green area that showed the grassy hills of Derbyshire, England. Nestled in the rolling hills were the town of Castleton and a historic castle called Peveril. “The fluorite is found in two caves to the west. One cave is named Treak Cliff, and the other is called Blue John. Inside the caves, the fluorite runs in veins that are as thick as your fist. The fluorite always has bands of colors like blue and purple or white and yellow.”
“Because of its beauty,” he said rolling the map and placing it back into the cylinder, “the Blue John Fluorite was largely mined and used to make jewelry, statues, and vases.” The group kept walking. Soon they were standing in front of a thick, woven mass of vines that looked like a door covering. “This is where you’ll find the Blue John Fluorite,” Mr. M said.
You can find out more about the first book in the Crystal Cave Adventures book series, Blue John’s Cavern, on our website.
Check out our website www.MiniMeGeology.com for great cubic fluorite samples and fluorite octahedrons. If you have questions about fluorite or any of our samples, contact us! We are happy to help you discover new, exciting samples for your collection.
Filed under: Minerals & Crystals on February 27th, 2020 | 2 Comments »
The release of the Crystal Cave Adventure series is an exciting step that blends fun adventure stories with science. In today’s world when Science, Technology, Engineering, and Math (STEM) curriculum is all the rage, a novel series that can transport kids to a story that is fictional yet has a touch of real science woven throughout the series is a welcome change to many children.
