Perhamite is a
phosphate mineral with the formula
Ca3 Al7(SiO
4)
3(
P O4)
4(OH)
3·16.5(
H2O).
It occurs in rare isolated masses in
amblygonite-rich
pegmatite
A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...
deposits throughout the world. It was discovered in platy sheed form of 1mm hexagonal crystals.
[Mills,S., Mumme, G., Grey, I. and Bordet, P.(2006): The crystal structure of perhamite. Mineralogical Magazine 70,201-209][Frost, Ray L., Matt L. Weier, and Stuart J. Mills. (2007)A Vibrational Spectroscopic Study of Perhamite, an Unusual Silico-Phosphate, Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy 67.3, 604-10] It was first described in 1977 by P.J. Dunn and D.E. Appleman
[Dunn, P. and Appleman, D.: Perhamite, a new calcium aluminum silico-phosphate mineral and a re-examination of viseite. Mineralogical Magazine 41, 437-442] from
pegmatite
A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...
collected from Bell Pit,
Newry, Maine
Newry (; ) is a resort town in Oxford County, Maine, United States. The population was 411 at the 2020 census. Newry was the site of one of Maine's worst Cold War aircraft crashes. The town is the home of Sunday River Ski Resort and has a p ...
. Other specimens have been found in
Kapunda, South Australia, in Silver Coin mine near
Humboldt County, Nevada[ and various locations throughout Europe.][
]
Composition
The formula[ Ca3 Al7(SiO4)3( P O4)4(OH)3·16.5( H2O) was determined by measuring its composition with x-ray spectroscopy giving the average amounts of SiO2 to be 13.72%, Al2O3 to be 27.17%, CaO to be 12.81%, P2O5 to be 21.61%, leaving 24.69% to be determined as H2O.][Mills, S. (2003): A note on perhamite from the Moculata( Klemms)phosphate quarry, South Australia, Australia. J. Mineral. 9, 43-45] The formula's essential elements are Al, Ca, H, O, P and Si with trace amounts of Sr. Common impurities of perhamite include Ti, Fe, Mg, Na, and F.[
]
Physical properties
Perhamite can range in color from white to brown and can be translucent to opaque. Its luster is said to be earthy, but vitreous to pearly along fractures. It occurs as radial discoidal, platy hexagonal crystals, in rough spherules up to 1mm thick.[ The specific gravity of perhamite is measured at 2.64][ with a calculated density of 2.53. It is structurally related to minerals in the crandallite subgroup, namely Iangreyite.][Mills, S.J., Kampf, A.R., Sejkora, J., Adams, P.M., Birch, W.D., Plášil, J. (2011): Iangreyite: a new secondary phosphate mineral closely related to perhamite. Mineralogical Magazine, 75, 327-336.]
Origin of the name
Perhamite is named after Frank Croydon Perham (born 1934), an American geologist and pegmatite miner of West Paris, Maine
West Paris is a town in Oxford County, Maine, United States. Originally settled in 1771 for land that what was deemed "superior for pasturage, hay crops, and orchards", West Paris became a center of Finnish ( fi, suomalaiset, ) immigrant sett ...
who is currently part of the faculty of The Maine Pegmatite Workshop and has over 45 years experience in mining pegmatites.
See also
* List of minerals
References
{{Phosphate minerals
Aluminium minerals
Phosphate minerals
Trigonal minerals
Minerals in space group 164