Biotite is a common rock forming mineral, being present in at least some percentage in most igneous and both regional and contact metamorphic rocks. The typical black to brown color of biotite is characteristic although it is difficult to distinguish brown biotite from dark brown phlogopite. The two are actually end members in a series that is dependent on the percentage of iron. Phlogopite is iron poor and biotite is iron rich. The darker color and density increase with an increase in the iron content.
Biotite tends to form in a wider range of conditions than phlogopite which is limited mostly to ultramafic rocks and magnesium rich marbles and pegmatites. Biotite, like other micas, has a layered structure of iron magnesium aluminum silicate sheets weakly bonded together by layers of potassium ions. These potassium ion layers produce the perfect cleavage.
Biotite is rarely considered a valuable mineral specimen, but it can accompany other minerals and compliment them. In Bancroft, Ontario Biotite forms large crystals with green apatite and hornblende. Single large plates or "books" of biotite can grow to considerable size and can make impressive mineral specimens. Weathered tiny crystals of biotite can appear golden yellow with a nice sparkle producing a "fool's Gold" that has fooled many.
Origin Of The Name
Biotite was named by J.F.L. Hausmann in 1847 in honour of the French physicist Jean-Baptiste Biot, who, in 1816, researched the optical properties of mica, discovering many unique properties.
Biotite mica is sometimes called "iron mica" because it is more iron-rich than phlogopite. It is also sometimes called "black mica" as opposed to "white mica" (muscovite) ? both form in some rocks, in some instances side-by-side.
Biotite has radioactive elements in it that age used to figure out how old the mineral is.
Sheets of biotite are flexible they can be bent and they go back to their original shape.
Mica posseses great resistance to the passage of electricity and heat and is therefore used as an electronic insulator.
Where Is It Found
Biotite is found in a wide variety of igneous and metamorphic rocks. For instance, biotite occurs in the lava of Mount Vesuvius and in the Monzoni intrusive complex of the western Dolomites. It is an essential phenocryst in some varieties of lamprophyre.
Biotite is occasionally found in large cleavable crystals, especially in pegmatite veins, as in New England, Virginia and North Carolina. Other notable occurrences include Bancroft and Sudbury, Ontario. It is an essential constituent of many metamorphic schists, and it forms in suitable compositions over a wide range of pressure and temperature.
The largest documented single crystals of biotite is approximately 75 sq ft sheets found in Iveland, Norway.
What Do We Do With It
Biotite is used extensively to constrain ages of rocks, by either potassium-argon dating or argon-argon dating. Because argon escapes readily from the biotite crystal structure at high temperatures, these methods may provide only minimum ages for many rocks. Biotite is also useful in assessing temperature histories of metamorphic rocks, because the partitioning of iron and magnesium between biotite and garnet is sensitive to temperature.
Mica posseses great resistance to the passage of electricity and heat and is therefore used as an electronic insulator. Micas have their main industrial use in the field of electronics. It is used as an insulating material since is does not transfer heat or energy very well. Mica is being used more and more in areas of very high heat levels such as rockets and missiles. Scrap, ground mica can be used to make heat-insulating bricks, as a filler for rubbers, and sometimes in the plant and lubricant and plastic industries. It is also used in making roofing material, wallpaper, lamp shades, etc.
With its low coefficient of expansion, its heat resisting properties make it a common demand to be used in production of fireproofing and insulating materials. Also can be used as a lubricant.
Mica is widely distributed and occurs in igneous, metamorphic and sedimentary regimes. Large crystals of mica used for various applications are typically mined from granitic pegmatites. Mica grows by building up see-through paper-thin layers upon layers, which appear opaque but are in fact transparent. Mica is very metallic (containing very reactive element metals such as Potassium and Lithium, as well as Aluminium and Silica) and can be cold to touch. Mica occurs semi-translucent crystals, either flat angular blades, or rosettes or even hexagonal thin columns. The soft, shiny and reflective layers that make up Mica reflect the many layers of consciousness present within life. These layers are voluminous and ever-changing such as: victim consciousness, blame, inhumanity, ego, forgiveness, growth, joy, nature, fashions, desire, creation and love which all co-exist.
Mica provides us with reflective qualities so that we can recognise the flaws of our humanity while staying heart centred so that we can love what we see here. It helps us to see situations in complete detail, highlighting areas of the greatest importance.
Mica is a wonderful energy to use when looking at yourself as it allows us to see that what you see in others and label, is what you choose to see, this allows us to see ourselves in others and eliminate patterns we do not like and embrace the ones we do. The clearer our vision becomes the more unified we are as the veil of separation disintegrates.
Mica enhances flexibility in all situations, helping us eliminate anger, tantrums and nervous energy. It helps release energy blocks within the body and align the chakras. Mica can be used for clarity in visions. The stones in the Mica family have the same healing abilities as mica but also have healing properties of their own.
Color: Black to brown and yellow with weathering.
Luster: Vitreous to pearly.
Transparency: Crystals are transparent to translucent.
Crystal System: Monoclinic; 2/m
Crystal Habits: Tabular to prismatic crystals with a prominent pinacoid termination. Biotite's four prism faces and two pinacoid faces form pseudo-hexagonal crystal "books". The sides of the crystal often tend to tapper and can have a "hard candy that has been sucked on, look". Also as lamellar or granular rock forming masses providing the luster for most schists and gneiss.
Cleavage: Perfect in one direction producing thin sheets or flakes.
Fracture: Not readily observed due to cleavage but is uneven.
Specific Gravity: Approximately 2.9 - 3.4+ (slightly above average)
Associated Minerals: Quartz, feldspars, apatite, calcite, hornblende, garnets and Schorl.
Other Characteristics: Cleavage sheets are flexible and elastic, meaning they can be bent and will flex back to original shape.
Best Field Indicators: Crystal habit, color, cleavage, elastic sheets and associations.