Description
Genuine Biotite Mica Mineral Specimen from Norway
This Biotite Mica mineral specimen from Norway is a carefully selected natural piece showcasing the classic layered structure and dark lustre that make biotite one of the most recognisable mica minerals. The specimen shown in the listing photographs is the exact piece you will receive, allowing collectors to view the natural crystal habit, reflective surfaces, and matrix characteristics before purchase. Full sizing and scale are shown in the listing photos.
Each specimen includes a Certificate of Authenticity lifetime guarantee generic card, confirming that this is a genuine natural mineral specimen. Biotite mica is valued by mineral collectors, geology enthusiasts, and educational collections for its distinctive sheet-like cleavage and common occurrence in igneous and metamorphic rocks.
Mineral Species and Chemical Composition
Biotite is a member of the mica group of silicate minerals, specifically classified as a phyllosilicate due to its layered crystal structure. Its composition varies naturally, but biotite is commonly described by the general formula K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂, reflecting varying proportions of magnesium and iron.
Biotite crystallises in the monoclinic crystal system, although it typically occurs as tabular, platy crystals rather than well-formed geometric crystal shapes. The defining feature of biotite is its perfect basal cleavage, meaning it splits easily into thin flexible sheets along flat planes.
This cleavage is a result of weak bonding between layers in the mineral structure, giving mica minerals their characteristic flake or sheet appearance.
Appearance, Colour and Physical Characteristics
Biotite is most commonly found in dark brown, black, or deep greenish-black tones, with a shiny reflective surface. When light hits the cleavage planes, the mineral can display a strong vitreous to pearly lustre.
Typical characteristics include:
• Colour: Dark brown to black, sometimes greenish-black
• Lustre: Vitreous to pearly on cleavage surfaces
• Transparency: Transparent in very thin sheets, opaque in thicker masses
• Crystal system: Monoclinic
• Cleavage: Perfect basal cleavage into thin sheets
• Hardness: Approximately 2.5 to 3 on the Mohs scale
Many specimens show stacked plates or book-like formations where the mineral layers are clearly visible. Depending on the host rock, biotite may occur as scattered flakes, larger “books,” or aggregated masses.
Geological Formation and Associated Rocks
Biotite is a common rock-forming mineral that develops in a wide range of geological environments. It forms primarily in:
• Igneous rocks such as granite, diorite, and other intrusive rocks
• Metamorphic rocks such as schist and gneiss
• Pegmatites, where large mineral crystals can grow
In igneous environments, biotite crystallises as magma cools, often alongside minerals such as quartz, feldspar, hornblende, and muscovite. In metamorphic environments, biotite forms through recrystallisation under heat and pressure, commonly appearing in mica-rich schists where mineral alignment can create foliation.
The presence of biotite can provide clues about the temperature and chemical conditions under which the host rock formed.
Norway Locality and Geological Context
Norway is well known among mineral collectors for a variety of pegmatite and metamorphic mineral localities. The country’s geology includes extensive Precambrian crystalline basement rocks, as well as numerous pegmatite fields that have produced collectible minerals.
Norwegian biotite specimens are often found within mica schists, gneisses, and granitic pegmatites, where mica minerals occur in well-developed sheets and clusters. These environments support large crystal growth and strong mica cleavage, making for attractive display specimens.
Collector Interest and Display
Biotite mica specimens are popular because their layered structure is visually striking and easy to demonstrate in a collection. They are frequently used for:
• Mineral and crystal collections
• Educational geology displays showing cleavage and phyllosilicate structure
• Natural history cabinets and rock collections
• Study specimens for identifying mica minerals
The reflective cleavage faces and “book” formations make biotite especially eye-catching under natural or indoor lighting.
Authentic Specimen and Item Details
• Genuine Biotite Mica mineral specimen
• Mineral group: Mica (phyllosilicate)
• Origin: Norway
• Dark brown to black colour with reflective cleavage surfaces
• Natural sheet-like crystal structure and perfect basal cleavage
• Carefully selected individual specimen
• The exact specimen shown in the photographs is the one you will receive
• Includes Certificate of Authenticity lifetime guarantee generic card
• Full sizing and scale visible in listing photographs
This Biotite Mica specimen from Norway is an excellent natural example of mica mineral structure, offering strong visual appeal and clear geological characteristics for collectors and educational displays alike.
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