<P> Garnets are nesosilicates having the general formula X Y (Si O). The X site is usually occupied by divalent cations (Ca, Mg, Fe, Mn) and the Y site by trivalent cations (Al, Fe, Cr) in an octahedral / tetrahedral framework with (SiO) occupying the tetrahedra . Garnets are most often found in the dodecahedral crystal habit, but are also commonly found in the trapezohedron habit . (Note: the word "trapezohedron" as used here and in most mineral texts refers to the shape called a Deltoidal icositetrahedron in solid geometry .) They crystallize in the cubic system, having three axes that are all of equal length and perpendicular to each other . Garnets do not show cleavage, so when they fracture under stress, sharp irregular pieces are formed (conchoidal). </P> <P> Because the chemical composition of garnet varies, the atomic bonds in some species are stronger than in others . As a result, this mineral group shows a range of hardness on the Mohs scale of about 6.5 to 7.5 . The harder species like almandine are often used for abrasive purposes . </P> <P> For gem identification purposes, a pick - up response to a strong neodymium magnet separates garnet from all other natural transparent gemstones commonly used in the jewelry trade . Magnetic susceptibility measurements in conjunction with refractive index can be used to distinguish garnet species and varieties, and determine the composition of garnets in terms of percentages of end - member species within an individual gem . </P> <Ul> <Li> Almandine: Fe Al (SiO) </Li> <Li> Pyrope: Mg Al (SiO) </Li> <Li> Spessartine: Mn Al (SiO) </Li> </Ul>

Where is garnet found in the united states