The chemical formula of mineral Bertrandite is indicated by Be4Si2O7(OH)2 or Beryllium Silicate Hydroxide. Bertrandite is actually a Silicate mineral. Mineral species Bertrandite was named after Leon Bertrand (1844-1909), a French mineralogist. It was first discovered in the year 1883 near Nantes, France. Bertrandite is known to crystallize in the orthorhombic system. In optical mineralogy, this orthorhombic crystal system comprises crystals having three mutually perpendicular axes, of which all are of different lengths.
Crystals of Bertrandite are usually found transparent to translucent in appearance. The crystal habit of Bertrandite as described in optical mineralogy usually include tabular to platy crystals and sometimes in prismatic forms, which can be very interesting when viewed with the aid of polarizing light microscopes for mineralogists. In optical mineralogy, tabular forms are described as crystals that are shaped like a book and this is usually very nice when viewed under polarized microscope used in optical mineralogy. The dominant faces of prismatic crystals are those of a prism and this can be seen clearly visible when evaluated with the aid of petrographic polarizing light microscopes. They are also often found as aggregates formed over crystals of Beryl. It commonly shows lamellar, parallel growth of individual crystals. Berlinite is considered as one of the more important ores of beryllium, but only secondary to mineral Beryl. Aside from being an ore of the same metal, Bertrandite mineral is also closely tied to the gemstone mineral Beryl. It has been known in mineral world that Beryl and Bertrandite are commonly associated with one another. In the field of optical mineralogy, it has been known that Bertrandite is actually an alteration product of mineral Beryl. Bertrandite can be found growing with Beryl crystals at some time. At some other times, Bertrandite can be found completely replacing the crystals of mineral Beryl to form a pseudomorph. In optical mineralogy, a pseudomorph is produced by the replacement of the chemistry and structure with a new mineral, but the outward shape of the original crystal is actually preserved. Some other pseudomorph is through an atom by atom replacement of one mineral for another. A pseudomorph is actually a false shape.
Mineral specimens of Bertrandite are commonly found colorless, white and pale yellow and is more clearly exhibited when evaluated under petrographic polarizing light microscope. They are commonly found colorless in thin sections. In optical mineralogy, it has been described that the colorless mineral specimens commonly allow the whole constituents of the white light to pass through making the mineral non-pleochroic even between crossed nicols of petrographic polarizing microscope for mineralogists. They commonly exhibit vitreous to pearly luster when viewed in reflected light of polarized microscope used in optical mineralogy. Bertrandite is most commonly found exhibiting a good cleavage in one direction lengthwise when the mineral section is closely evaluated under polarizing light microscope for mineralogists. Sometimes it can be also found perfect. Bertrandite also usually shows uneven to conchoidal fracture when viewed under several adjustments on the aperture diaphragm of the petrographic polarizing microscope. The specific gravity measure of Bertrandite mineral is commonly found ranging from 3.3 grams per cubic centimeters to 3.5 grams per cubic centimeters. The hardness measure for mineral Bertrandite using the Mohs scale method is usually found ranging from 6 to 7. Bertrandite is most commonly found leaving a white to gray streak when it is rubbed on a white steak plate. Bertrandite crystals are usually found brittle, a property commonly displayed by glasses and most non-metallic minerals.
Bertrandite specimens are most commonly found showing a moderate surface relief when closely evaluated under several adjustments on the aperture diaphragm of the polarizing light microscope for mineralogists. It shows very weak dispersion when viewed in plane light of petrographic polarizing microscope. Bertrandite mineral crystals are also most commonly found showing a biaxial negative figure when viewed between crossed nicols of petrographic polarizing microscope used in optical mineralogy. Crystals of Bertrandite mineral as described in the field of optical mineralogy are commonly twinned. These twinned crystals are most commonly found more splendidly exhibited when viewed under polarizing microscopes for geologists. Twinned sections can be seen clearly visible between crossed nicols of polarized light microscope for mineralogists. A possible sequence of polysynthetic twinning can be also possibly found. Often times, twins are found as heart shaped and these are seen clearly visible when viewed under polarizing light microscopes used in optical mineralogy. When evaluated using the cobalt nitrate test, Bertrandite usually turns blue. Bertrandite crystals commonly whiten but hardly fuse on charcoal and are often found insoluble in acid. Specimens of Bertrandite are usually found exhibiting fluorescent green color under ultraviolet light. There is no specific data on the toxicity and health danger for mineral Bertrandite. However, specimens of this mineral should be treated with great care and use of sensible precaution is advised upon handling them.
Bertrandite mineral is commonly associated with quartz, micas, cheralite, albite, fluorapatite, fresnoite, orthoclase, anatase, pyrite, calcite, brookite, analchime and top most of all of course the Beryl mineral. The best field indicators of Bertrandite mineral commonly include color, hardness, cleavage, crystal habit and its splendid association with mineral Beryl. Bertrandite mineral is commonly found in beryllium bearing pegmatite rocks and also in some hydrothermal veins. It is also considered as a secondary mineral, which is mostly formed from late post-deposition hydrothermal attack on pegmatite Beryl. It can be also found as primary from lower-temperature gas deposition that is causing a rock alteration. Bertrandite minerals can be also found in fissures in granites and pegmatites and in miarolitic cavities in greisens. Bertrandite notably occurs in types of localities such as France, Kazakhstan, Russia, Utah, New Mexico, California, China, England, Norway, Mexico and Mongolia. Excellent small Bertrandite crystals are found in pockets in the cleavelandite feldspar at Portland, Connecticut.
