The chemical formula of mineral Allanite is indicated by (Ca, Ce, La, Y)2(Al, Fe)3(SiO4)3(OH), a Calcium Cerium Lanthanum Yttrium Aluminum Iron Silicate Hydroxide. Allanite is actually a Silicate mineral. It was discovered in the year 1880 in Aluk Island, Greenland. It was named Allanite in honor to the Scottish mineralogist Thomas Allan (1777-1833). Some authors sometimes referred mineral Allanite as a trash cam mineral because it has the capability to possess or attract unwanted elements of other minerals. There are three minerals known to as listed in the Allanite group by the International Mineralogical Association. Each is recognized as a unique mineral through their composition depending on what rare earth element is present. The Cerium rich Allanite known as Allanite- (Ce) is the most common Allanite, which is most often referred to as Orthite, or simply Allanite. The Lanthanum rich Allanite is known as Allanite- (La). The Yttrium rich Allanite is known as Allanite-(Y). A chemical test is required in order to differentiate one from the other because they almost have the same structures with only slight variations on their several properties. Allanite is also a known member of the Rare Earth minerals. Allanite mineral in Europe is known to be orthite. Allanite is considered as a potentially valuable ore, which is up to 20 percent Rare Earth elements in composition. Traces of Thorium in Allanite make the mineral slightly radioactive. An evidence of the radioactive effects of nearby minerals to Allanite is the presence of the halo or dark ring in the embedded crystals of the mineral, which can be seen clearly visible when the mineral is viewed between crossed nicols of petrographic polarizing light microscope used in the field of optical mineralogy. Allanite may become metamict due to disruption of the structure caused by decay of radioactive elements in the mineral. This metamict Allanite minerals turns out to often contain substantial amounts of adsorbed water. However, the strongly metamict varieties of Allanite mineral is known to be very low. Since mineral Allanite is known to be slightly radioactive, it should be stored away from other minerals that are prone to damage from radioactive elements. Human exposure should also be limited.

 

            Mineral Allanite is also known to crystallize in the monoclinic crystal system, which can be seen clearly when specimen is evaluated with the aid of polarized light microscope for geologists. In the field of 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. Mineral Allanite crystals are commonly found opaque in appearance but sometimes can be also translucent. They are usually disseminated in igneous rocks. Often found as small-embedded grains in igneous rocks and some other metamorphic rocks. It sometimes exhibits a tabular crystal form, which is interestingly visible when viewed under a polarizing microscope for geologists showing a splendid form and character. Allanite is usually found having a biaxial negative figure when evaluated between crossed nicols of petrographic polarizing light microscopes used in the field of optical mineralogy. The highest interference color in thin sections is usually upper first- or second-order colors that are splendidly displayed in plane-polarized light of polarizing microscope for mineralogists. The brown color of the mineral often masks the interference colors that can be found when mineral Allanite is examined between crossed nicols of polarizing microscopes in optical mineralogy. Strongly metamic varieties maybe sensibly isotropic and have low indices. Chemical zoning may be expressed by variation in birefringence and it can be clearly found visible when viewed in plane-polarized light of petrographic polarizing microscopes used in the field of optical mineralogy.

 

            Mineral Allanite has moderate to high surface relief when it is evaluated under minor adjustments of the aperture diaphragm of polarized light microscope for mineralogists. As traces amounts of iron increases, both indices of refraction and birefringence also increases. This mineral is rarely twinned, though twinning on several angles can be found when the mineral is evaluated with the aid of polarizing microscopes used in optical mineralalogy. Longitudinal sections show parallel extinction and are fast length, which can be seen clearly exhibited between crossed nicols of polarized light microscope for mineralogists. Crystal formation of mineral Allanite has splendid view under petrographic polarizing microscopes and usually showing variations from euhedral to subhedral form. They may appear bladed, columnar, or sometimes acicular and elongate at parallel axis that is splendidly exhibited under polarizing microscopes in optical mineralogy field. Sometimes they may appear anhedral grains or granular aggregates, which are commonly exhibiting nice and interesting microscope images under polarized microscope for mineralogists.

 

            The fracture found when mineral Allanite is evaluated under polarizing microscopes used in the field of optical mineralogy is commonly conchoidal. There is some fracture perpendicular to the length of crystals that may be filled with quartz. Hand samples may appear light brown, dark brown, or black. Mineral Allanite commonly exhibits vitreous to pitchy luster in reflected light of the polarizing petrographic microscopes for mineralogists. Pleochroism is distinct in a variety shades of brown, red brown, yellow-brown, or less commonly, greenish brown or green when the mineral is viewed in plane-polarized light of petrographic polarizing microscope used in optical mineralogy. There is one fair cleavage found in one direction and poor cleavage on the other two directions when the mineral is evaluated under several adjustments on the aperture diaphragm of polarizing microscopes. It is clearly visible under petrographic microscopes that cleavages of this mineral are not really well developed. Mineral Allanite commonly shows black streak when rubbed on a white porcelain streak plate. The hardness measure of the mineral using the Mohs scale method is usually 5.5. The specific gravity measure of the mineral is approximately 3.0 grams per cubic centimeters to 4.2 grams per cubic centimeters giving an average of 3.6 grams per cubic centimeters.

 

Allanite minerals are commonly found as accessory mineral in granite, granodiorite, diorite, syenite, nepheline syenite, pegmatite, and other equivalent volcanic rocks. It is closely associated with boitite, hornblende, or other mafic silicates. It is also found as accessory mineral in gneiss, schist, granitic gneiss, amphibolite, or occasionally in skarns or other metamorphosed carbonate rocks.