Gahnite, ZnAl₂O₄, is a rare mineral belonging to the spinel group. It forms octahedral crystals which may be green, blue, yellow, brown or grey. It occurs in Falun, Sweden where it is found in pegmatites and skarns, contact metamorphic rocks. Other occurrences include Charlemont, Massachusetts; Spruce Pine, North Carolina; White Picacho district, Arizona; Topsham, Maine; and Franklin, New Jersey in the United States. It was named after the Swedish chemist, Johan Gottlieb Gahn (1745-1818) the discoverer of the element manganese. It is sometimes called zinc spinel. Spinel is one of a group of minerals which crystallize in the isometric system with an octahedral habit, and whose chemical compositions are analogous. ... Pegmatite is a very coarse-grained igneous rock that has a grain size of 20 mm or more; such rocks are referred to as pegmatitic. ... Skarn is a fine grained metamorphic rock that is usually variably colored green or red, occasionally grey, black, brown or white. ... Metamorphic rock is the result of the transformation of a pre-existing rock type, the protolith, in a process called metamorphism, which means change in form, derived from the Greek words meta, change, and morphe, form. The protolith is subjected to extreme heat (>150 degrees Celsius) and pressure causing profound... Charlemont is a town located in Franklin County, Massachusetts. ... Spruce Pine is a town located in Mitchell County, North Carolina. ... Topsham is a town located in Sagadahoc County, Maine. ... Franklin is a borough located in Sussex County, New Jersey. ... Johan Gottlieb Gahn discovered manganese in 1774. ... General Name, Symbol, Number manganese, Mn, 25 Chemical series transition metals Group, Period, Block 7 , 4, d Density, Hardness 7470 kg/m3, 6. ...

References

• Mindat (http://www.mindat.org/min-1632.html)
• Webmineral (http://webmineral.com/data/Gahnite.shtml)
• Mineral Galleries (http://mineral.galleries.com/minerals/oxides/gahnite/gahnite.htm)