Fluorite

Besides being one of the most popular minerals for collectors (known as "the most colorful mineral in the world"), fluorite is a very important raw material for many industries, with uses as diverse as a flux for smelting metals (hence the name, from the Latin for "to flow"), refining uranium fuel for nuclear reactors, oil well stimulation, and making rocket fuel; to adding fluorite to toothpaste and making herbicides, medicines, anesthetics, and special lenses for long-range telescopes -- and much more. It's also used to create opalescent glass -- melted into molten glass, it separates out into tiny crystals of sodium fluoride which bounce the light around inside the glass, creating opalescence.

Not only is fluorite found in a dazzling array of colors -- blue, green, yellow, purple, magenta, red, black, brown, pink, and most everything in between -- but some specimens have the added effects of simultaneously glowing a different color under shortwave and longwave UV light, and phosphorescing a third color (the term fluorescent is derived from the mineral fluorite). Still others are thermoluminescent (glowing when heated)! The purest fluorite is colorless, but the presence of impurities in the hydrothermal solution containing fluorine that was forced through fissures in the earth hundreds of years ago, melting calcium-rich rocks to re-form as fluorite, created the rainbow of colors we see today.

Chlorophane, a variety of fluorite, will actually glow green in a dark room when activated by the heat of a person's hand -- but only once! That same specimen will never glow again, because electrons that were trapped in an excited state during crystallization have been allowed to "relax" after emitting the photons of light. So, if a piece of fluorite ever glows in your hand, don't try to reproduce it for anyone else with the same piece -- they'll think you're crazy!

Fluorite is also formed in a wide variety of shapes and patterns. The cube is the typical crystal habit, with uncleaved octahedrons forming much less often, and penetration twins creating more complex shapes. Perfect cleavage in four directions creates one of the favorites of collectors both young and old -- fluorite octahedrons, or "fluorite diamonds". Fluorite mine workers are reported to cleave octahedrons on their lunch breaks for extra cash.

The range of metaphysical uses for fluorite is no smaller than its range of colors. In general, it is believed to clear the mind, heighten the ability to concentrate, and encourage orderliness. Therefore, a chunk or slab of fluorite makes a great addition to your desk and a terrific gift for a student. Here's a breakdown of the uses of some other popular colors:
 
Blue: creates order, calm, and clear concise communications
Sea Green: clears emotional baggage and eliminates negativity
Purple: a third-eye stone; brings order to psychic and spiritual growth
Bright Green: creates a connection with ones environment and attracts money
Colorless: stimulates the brain and clears and energizes the aura

Fluorite: CaF2, Calcium Fluoride (also known as Fluorospar)
Hardness: 4
Luster: vitreous
Transparency: transparent to translucent
Cleavage: perfect in 4 directions, forming octahedrons
Fracture: irregular and brittle
Specific gravity: 3.1+ (average)
Streak: white
Other: often fluorescent, displays color zoning

What Makes Rocks Fluoresce

Under the rays of a UV lamp many ordinary items fluoresce: teeth, white shirts, many inks and plastics, crankcase oil, some woods -- even scorpions, a fact which has caused problems for more than one prospector who was out hunting the desert at night! But it is the response of fluorescent minerals that excites the interest of collectors. Calcite, which is often a dull white in ordinary daylight, may fluoresce red or orange red, pink, or green. Fluorite is pretty on its own, but really comes alive under UV: bright pale yellow, deep green, blue-green, blue, violet-blue, red-violet, orange, cream, and bluish white.

The fluorescent color variations displayed by a mineral are generally due to impurities known as activators. The activator (or activators, in some cases) absorbs ultraviolet radiation, and in reaction emits a combination of visible light (color) and minute amounts of heat. The activator manganese makes calcite fluoresce red or orange-red; fluorite, a deep green; and fluorapatite, yellow. The uranyl ion makes most minerals in which it is found fluoresce some shade of green. In other rocks, europium ions may be responsible for a blue glow, and yttrium for yellow.

Sometimes the activator electrons get stuck in their high-energy state, and the mineral will continue to glow after the UV light is switched off. This is called phosphorescence. The variety of Willemite found in Franklin, NJ is an excellent example of a mineral that is both fluorescent and phosphorescent, but there are many others. Calcite is often phosphorescent. Applying heat to some UV-charged minerals (by holding them briefly under a hot water tap, for example) will make the phosphorescence even more dramatic.

Collecting Fluorescent Minerals
Often the most satisfying way of acquiring specimens is to find them yourself. One good way to start is to join a local rock club. If none is available, or you prefer to go it alone, a good book on fluorescent minerals, combined with a rockhounding guide to your area can get you started. Always be sure that you know the status of the area where you plan on collecting, and get permission when it is needed! A good resource for both the beginning and the experienced prospector is the Fluorescent Mineral Society.

Small handheld 4 watt UV lamps are convenient and easy to carry. They are a good place to start when you are new to the hobby. The larger 6 watt handhelds will be more satisfying to the committed prospector, as they will trigger fluorescence in specimens from several feet away, a great boon when you are out hunting at night. Multiband or combo lamps allow the user to switch between short-wave and long-wave light. This can provide a significant savings in the cost of your equipment, though some decrease in ultraviolet output can be expected.

Other tools useful to the UV mineral prospector are standard rockhounding tools: hammers, chisels, pry bar, field bag, safety equipment, and the like. Safety glasses or goggles will protect your eyes from short-wave radiation as well as flying rock chips, and a good flashlight should go along with your UV lamp(s) for night trips.

Some way of creating a dark space for testing possible fluorescent specimens is necessary when prospecting during daylight hours. Commercial viewing bags are available, though a black plastic sheet does a pretty decent job and is both lightweight and inexpensive. When wrapping your prizes (which you should always do before you put them in your field bag), either wrap them first in plastic wrap, or be sure that you've tested the newspaper you plan to use for fluorescent dyes.

Read the rest of this article in our Learn More About Rocks & Minerals section.

How to Clean Quartz

With a little luck, you'll come across some quartz crystals in your rockhounding adventures this summer. Newly dug quartz crystals and crystal formations are often stained red-brown from iron and crusted with clay, when they're not coated with tougher substances such as limonite or calcium deposits. Getting these off to display the sparkling beauty beneath can be a lot of work, but the right techniques and cleaners will help.

Initial Cleaning
The first step is to get rid of the clay. For a few prize specimens, tools such as an old toothbrush and bamboo shish kebab skewers will do the job. If you have many to clean, however -- particularly if they are intricate formations -- leave them to dry in the shade until the clay cracks. Then hose them off with your spray nozzle set for as much pressure as possible. Often you will need to repeat this step several times, allowing the clay to completely dry again between hosings.

Tip: Don't do this in your sink or bathtub! Clay will clog your pipes.

If your sample has organic material on it, like algae, use household bleach to clean it. Be sure to let it dry for a day before using any acid cleaning method.

Cleaning with Oxalic Acid
Here are some general safety rules for cleaning minerals with acid:

• Only use chemicals that are clearly labeled and store them in a secure area away from pets and children.
• Keep a large container of clear water handy to wash off any chemical spills.
• ALWAYS wear safety goggles & rubber gloves.
• Don't work alone.
• Avoid splattering.
• Never pour water into acid -- always add acid to water.
• Keep an ample supply of baking soda handy for acid spills.
• Rinse specimens well.

Getting Rid of Iron Stains
A common disfiguration of quartz crystals is a rusty staining caused by iron. Soaking the crystals in oxalic acid powder is the usual way to remedy this.

Start by putting your specimens in a plastic bucket after cleaning all the clay off them (clay keeps the acid from doing its job). Cover them with distilled water and add the oxalic acid powder. Follow the directions on the package if available. If not, you may have to try several different concentrations of solution for different soaking periods, depending on how stained your specimens are. You can start by adding 1/2 to 1 cup of oxalic acid crystals to 1/2 gallon of water in the bucket. For larger quantities, use about 16 ounces of oxalic acid to 2 gallons or more of water. Too much oxalic acid can turn quartz yellow, so if you have light staining, only use about 2 tablespoons of oxalic acid per 1/2 gallon of water. Always remember to add acid to water, not water to acid! Let your mineral specimens soak for one to several days, or, if you're in a hurry (or the staining is very heavy), you can heat the solution by standing the bucket in the hot sun. Some people use an old crock pot instead of a plastic bucket, and heat their acid solution that way. Don't heat this solution on your kitchen stove, and don't use any kind of metal container. Do this procedure outside, particularly if you heat (never boil) the acid, as it puts off poisonous fumes. Oxalic acid is mild as acids go, but rubber gloves are a good idea when handling either the acid solution or your specimens until they are well rinsed.

If the crystals start to develop a powdery coating as they dry, soak them in a baking soda solution -- about 1/3 cup to a gallon of water -- and then rinse them well. If they get a yellowish stain or coating during the process, soak the specimens in water for up to a week. For your next batch, try using a weaker solution of acid and stir the solution frequently.

The oxalic acid solution can be reused many times by just adding a little water and powdered acid each time. When it turns a deep green, you need a new batch. Neutralize the worn out solution by adding baking soda until the mixture stops fizzing. Then you can pour it down the drain or out on the ground.

Read about other quartz cleaning challenges and how to overcome them on our website.

Geology Word Puzzler

Vug is the name of a character in Philip K. Dick's sci-fi novel The Game-Players of Titan. But what does vug mean to a rockhound?

Vugs are small cavities inside rock that are formed when crystals form inside a rock matrix and are later removed through erosive processes, leaving behind voids. A common cause of vugs is minerals precipitating from solution in water, and then later being dissolved again by less saturated water. The inner surfaces of vugs are often coated with some of the mineral matter that formed them.  ~from Wikipedia

A geode is essentially a vug that has been removed intact from the original rock/matrix and has a rind and some type of coating (often amethyst or quartz crystals or druzy) on the inside.

The Vug is also the name of a terrific web reference for rockhounds!

We'd love to hear from you! Have questions or comments about the website, or just want to tell us about your latest rockhounding adventure? Email us at we_rock@mamasminerals.com!

Read about rose quartz, geodes, and identification of rocks and minerals in the Fall 2006 issue of RockZ NewZ

Read about rose quartz, geodes, and identification of rocks and minerals in the Summer 2006 issue of RockZ NewZ

Read about vanadinite, building fountains, and identifying meteorites in the Winter 2004 issue of RockZ NewZ.

Read about celestite, pearls, and how to choose the right rock tumbler in the Fall 2004 issue of RockZ NewZ.

Read about malachite, tumbling grits, and how to pan for gold in the Summer 2004 issue of RockZ NewZ.

Read about amethyst, fossil preparation, and field tools for the rockhound in the Spring 2004 issue of RockZ NewZ.

Read about galena, petrified wood, and collecting micrometeorites in the Winter 2003 issue of RockZ NewZ.

Read about iron pyrite, tumbling seaglass, and stony meteorites in the Summer 2003 issue of RockZ NewZ.

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