The chemical formula of mineral Gmelinite is indicated by (Na2, Ca)Al2Si4)12 – 6H2O or Hydrated Sodium Calcium Aluminum Silicate. Gmelinite is actually a Silicate mineral. It is also a known member of the Zeolites Group of minerals. Mineral species Gmelinite was named after Christian Gottlob Glemin (1792-1860), a German chemist and mineralogist. Gmelinite is most commonly found crystallizing in the hexagonal system of crystal formation. In optical mineralogy, the hexagonal system of crystallization comprises crystals having four axes. Three of which are positioned in a single plane with equal length and are symmetrically spaced. The fourth axis is found to be perpendicular to the other three axes. Gmelinite is most commonly used as mineral specimen and it often exhibits nice and interesting appearance when viewed under petrographic polarizing light microscope used in optical mineralogy. It is also commonly used as a chemical filter.
Mineral Gmelinite however is one of the rare zeolite minerals that are not really known so well in the mineral world. Zeolite minerals are known to possess the openness about its structure and this usually allows large ions and molecules to reside as well as move around its overall framework. These open channels allow large ions and water to travel in and out of the crystal structure. The size of the molecules and ions are actually controlled by the size of the open channels. Therefore, a Zeolite mineral like Gmelinite can actually act as a chemical sieve that allows some ions to pass through while blocking the others. Gmelinite crystals are commonly found having a unique shape. It is usually found hexagonal in outline and it is commonly dominated by a dipyramid where two identical pyramids are found at the top and bottom of the specimen. These are quite very interesting when viewed under petrographic polarizing light microscopes. However when the specimen is evaluated with the aid of geological polarizing light microscopes, the faces of the pyramids are relatively gentle in slope and are capped by a flat pedion face.
Gmelinite is most commonly found clear, white, pink, yellowish and reddish in appearance that can be more splendidly wonderful when viewed with the aid of polarizing light microscopes used in optical mineralogy. Gmelinite is most commonly found exhibiting a vitreous luster in reflected light of petrographic polarizing microscope for mineralogists. Gmelinite is known to have absent cleavage even when it is closely examined under several adjustments on the aperture diaphragm of petrographic polarizing microscopes. Gmelinite is most commonly found showing uneven fracture when it is evaluated with the aid of polarized microscopes used in optical mineralogy. The specific gravity measure of the mineral usually gives an approximate value ranging from 2.0 grams per cubic centimeters to 2.1 grams per cubic centimeters, which is considered very light. The hardness measure of Gmelinite when it is evaluated using the Mohs scale method is usually 4.5. Gmelinite is commonly found leaving a white streak when it is rubbed on a white porcelain streak plate.
Most Gmelinite crystals are found transparent to translucent in appearance. The crystal habit of Gmelinite as described in optical mineralogy usually include tabular to platy crystals with clear hexagonal outline that can be very clearly visible when viewed under polarizing light microscopes for mineralogists. The crystals of Gmelinite is usually found with a gently sloping hexagonal dipyramid that terminates the top and bottom of the crystal. Pinacoidal faces that are more clearly visible when viewed with the aid of polarizing microscopes for geologists often truncate these crystal faces. The overall effect is somewhat similar to the look of an angular classic UFO flying saucer. Twinning can be also found with a penetration twin that can be visibly clear when the mineral specimen is evaluated under geological polarizing light microscopes.
Gmelinite specimen can be found having vertical striations on the dipyramidal faces when it is evaluated between crossed nicols of petrographic polarizing microscopes used in optical mineralogy. Gmelinite is most commonly found exhibiting a moderate surface relief when it is evaluated under several adjustments on the aperture diaphragm of the polarizing microscopes for mineralogists. Gmelinite is commonly found showing uniaxial figure that can found either optically positive or negative when the specimen sample is evaluated evaluated between crossed nicols of petrographic polarizing microscopes. The maximum birefringence of the mineral is usually 1.474. The refractive index of the mineral when it is evaluated with the aid of petrographic polarizing microscopes is usually ranging from 1.474 to 1.494. There is no specific data found on the toxicity and health dangers for mineral Gmelinite. However, the specimens of this mineral species should be treated with great care and use of sensible precaution is advised upon handling them.
Gmelinite is most commonly associated with several interesting minerals including quartz, natrolite, stilbite, calcite, phillipsite, heulandite, chabazite and other zeolites. The best field indicators of mineral Gmelinite usually include associations, density, crystal habit and hardness. Mineral Gmelinite notably occurs at several types of localities including Glenarm in North Ireland, Siegerland in Germany, New Jersey and Faroe Islands.
