The chemical formula of mineral Zinnwaldite is indicated by KLiFeAl(AlSi3)O10(OH,F)2 or Potassium lithium iron aluminum silicate hydroxide fluoride. Zinnwaldite is actually a Silicate mineral. Zinnwaldite is most commonly used as mineral specimen and it has also limited use as electrical and heat insulator for industrial purposes. Zinnwaldite is usually found darker in color than typical muscovite but is usually lighter than Phlogopite or biotite when closely evaluated with the aid of petrographic polarizing light microscope used in the field of optical mineralogy. It has been found that the dark color and density in the three iron containing micas increase with an increase in the iron and magnesium content. It is sometimes difficult to distinguish Zinnwaldite form other micas when evaluated using ordinary methods, locality and environment of formation as keys to identification. It is usually limited to special granites and their pegmatites. Just like other micas, Zinnwaldite is usually found with layered structure of lithium iron aluminum silicate sheets that are weakly bonded together by layers of potassium ions. These potassium ions layers usually produce the perfect cleavage of the mineral that can be found more clearly visible when specimen sample is evaluated more closely under petrographic polarizing light microscopes used in the field of optical mineralogy. Zinnwaldite is rarely available to collectors but some nice specimens fund with apatite are now on the market showing nice tabular crystals.
Zinnwaldite is most commonly found pale brown to gray and even green in color that appears more fascinating and more splendidly exhibited when viewed with the aid of polarizing light microscopes for mineralogists. Zinnwaldite is most commonly found showing vitreous to pearly luster when viewed in reflected light of polarized microscope used in optical mineralogy. Most crystals of mineral Zinnwaldite are found transparent to translucent in appearance. Zinnwaldite is also known to crystallize in the monoclinic system of crystal formation. In optical mineralogy, the monoclinic system of crystal formation comprises crystals having three axes of unequal lengths. Two of which are usually found in a position that is oblique or not perpendicular to one another. However, both of which are commonly found perpendicular to the third axis. The crystal habit of mineral Zinnwaldite as described in the field of optical mineralogy include mostly of tabular crystals with a prominent pinacoid termination that can be found more clearly visible when viewed with the aid of petrographic polarizing light microscopes for mineralogists. It can be noticed that the four prism faces and two pinacoid faces of mineral Zinnwaldite can form pseudo-hexagonal crystal books that appears more interesting under polarizing microscopes used in the field of optical mineralogy. It can be also found that the sides of the crystal often tend to tapper when viewed with the aid of petrographic polarizing microscopes used in optical mineralogy. It can be also found as lamellar or granular rock forming masses. Mineral Zinnwaldite is usually found showing perfect cleavage in one direction producing thin sheets or flakes that can be found more early visible when viewed with the aid of polarizing microscopes used in the field of optical mineralogy. The fracture of mineral Zinnwaldite is not readily observed due to cleavage but when found using the petrographic polarizing microscopes used in optical mineralogy, it is usually uneven. The hardness measure of mineral Zinnwaldite when it is evaluated using the Mohs scale method is usually 2.5 to 3. The specific gravity measure of the mineral is approximately 2.9 to 3.2+ grams per cubic centimeters, which is considered average to slightly above average. Zinnwaldite is most commonly found leaving a white streak when rubbed on a white porcelain streak plate. It is most commonly found associated with other quartz, apatite, feldspars and tin minerals. The cleavage sheets of mineral Zinnwaldite are flexible and elastic. In optical mineralogy, this means that they can be bent and they will flex back to original shape. Thin flakes show an asterism or six rayed star when a light source is viewed through the crystal due to inclusions which can be found more clearly visible under petrographic polarizing microscopes. The best field indicators of mineral Zinnwaldite usually include color, crystal habit, cleavage, elastic sheets, associations and environment of formation. Zinnwaldite notably occurs at Cornwall in England, San Diego in California as well as Germany.
