STRENGITE

Greetings everyone; this month we will examine one of the prettier iron phosphates, the mineral Strengite. This mineral is an iron phosphate di-hydrate with a chemical formula of: FePO4 • 2H2O. Crystallizing in the Orthorhombic Dipyramidal class, Strengite is isostructrual with the iron arsenate di-hydrate Scorodite. The term ‘isostructural’ means the two mineral shares the same crystal form. Strengite also forms a chemical series with Varicite which is an aluminum phosphate di-hydrate. In terms of crystal symmetry, Strengite exhibits 2/m 2/m 2/m form. These numbers and letters mean that there are three dual mirror planes in the symmetry of the crystals of Strengite; or put another way, the crystals are highly symmetrical no matter which way you look at them.

Strengite is named for Johann August Streng (1830-1897), German mineralogist, University of Giessen, Germany. The most common occurrence of strengite is as spherical aggregates of rheniform masses. However strengite does occur in distinct crystals on the mineral dufrenite in Rockbridge county, Virginia and in distinct crystal groups from Indian Mountain, Cherokee County, Alabama. Crystals from this occurrence appear as pale violet sword-like crystals, singly and in stellate crystal groups. Color ranges from pale violet to pale red. Strengite makes excellent micromounts and the mineral is available from many mineral dealers at reasonable prices.

Shown below are some photomicrographs of Strengite from the High Bluff Limonite Bank, Indian Mountain, Cherokee County, Alabama. The photomicrographs were taken with a Nikon SLR on a trinocular microscope at 35X magnification. Kodak ASA 400 color print film was used with 4 second exposures using white LED illumination.




References:
Dana, E.S., Ford, W., A Textbook of Mineralogy, 1966,
John Wiley and Sons, New York, Page 723.
http://webmineral.com/data/Strengite.shtml
http://webmineral.com/data/Variscite.shtml