AUGELITE: AN UNCOMMON GREEN PHOSPHATE

The trouble with doing nothing is that you never know when you are finished.

Ah, another fairly rare phosphate mineral has popped up on my radar screen.  The other day, in a fit of doing nothing of importance, I spotted a photo of a sparkling faceted gemstone called augelite.  Somewhere from the back recesses of my mind a bell started ringing and forced my memory to “get in gear.”  Yep, now I remember that at a Tucson show I picked up a specimen of augelite from a Peruvian dealer: 1) it was a “pretty” specimen; 2) it was a phosphate mineral; 3) it was not in my mineral vocabulary; 4) it was reasonably priced; and 5) the dealer was a pleasant person.  Upon returning home I stuck the specimen in the drawer labeled South America #1 and promptly moved on to other “things.”  OK, my mind works in mysterious ways so I recently hauled out the specimen and again thought it was nice and decided to widen my mineral vocabulary!

 

A pale green crystal of augelite (A) attached to several gemmy quartz crystals (Q).  The C-axis runs the length of the crystal.  See below. Maximum length of crystal is ~1 cm.

A computer-generated crystal of augelite.  Compare with photo above.  Note C axis runs length of crystal.  Image courtesy of  www.smorf.nl.  Original drawing in V.M. Goldschmidt, Atlas der Krystallformen, 1913-1923.

Augelite is an uncommon hydroxyl aluminum phosphate [Al₂PO₄(OH)₃] that has been reported from several localities around the world but specimens on the market seem to come from just a few localities in in Bolivia, Peru, Canada (Dawson Mining District), and California (the now depleted Champion Mine).  In fact, most market specimens are from the "world’s best occurrence" at Mundo Nuevo Mina, Huamachuco, Sanchez Carrion Province, La Libertad Department, Peru (Moore, 1915).  The crystals from Mundo Neuvo are usually apple-green to colorless, transparent to semi-transparent, have vitreous to pearly luster, and are well developed. Crystals are commonly striated, have a white streak and are ~4.5 hardness (Mohs). Other localities have yielded colorless to white to pale yellow and even pale blue crystals. Most of the Peruvian specimens are intimately associated with quartz crystals and “needle quartz” is especially attractive.  Crystals are Monoclinic and commonly appear as thick tabs.

Augelite crystal shown above.  Note tiny terminated quartz crystal extruding from crystal face at end of arrow.  Length of quartz crystal is less than 1 mm.

“Augelite forms in a variety of situations including high-temperature Al-rich hydrothermal deposits, tin- and/or lithium-bearing pegmatites, hydrothermally altered andesites, Al-rich metaquartzites” (Visser and others (1997), “hydrogen metamorphism of phosphate-bearing rocks in peraluminous sediments” (AZO Mining, 2017) and by “metasomatic replacement of aluminosilicates minerals” (Wise, 1975).  I remain (after several hours of searching) uncertain about the geology of the Mundo Neuvo Mine.  At one time it produced hubnerite and scheelite so perhaps the initial target was tungsten?  According to Moore (2015), Mundo Neuvo was last used as a specimen mine (especially for augelite).

I noticed that augelite has been found in the Black Hills of South Dakota from the Rough and Ready Mine (Tinton District), and the Bob Ingersoll, Etta and Hugo mines in the Keystone District.  All localities are lithium-rich pegmatites so perhaps augelite formed from the alteration of primary lithium minerals?  At the famous Palermo #2 Pegmatite in New Hampshire, augelite forms as a high temperature (~500-300C), oxidizing to non-oxidizing, alteration product of montebrasite [LiAlPO₄(OH)], and in oxidizing to non-oxidizing, low temperature (~300-100 C) conditions (Nizamoff, 2006).  See previous posting on alteration of lithium-rich minerals.

So, augelite is another of those uncommon phosphate minerals that has entered my specimen vocabulary.  I look forward to a continued learning experience about rather exotic, at least in my collection, minerals.   

REFERENCES CITED

AZO Mining, 2017, Augelite-occurrence, properties and distribution: www.azomining.com.

Moore, T.P., 2015, What’s new in the Mineral World: The Mineralogical Record, Report #40.

Nizamoff, James, 2006, The Mineralogy, geochemistry and phosphate paragenesis of the Palermo #2 Pegmatite, North Groton, New Hampshire: University of New Orleans Theses and Dissertations, Paper 398.

Visser, D., R.O. Felius, and M. Moree, 1997, Augelite and cerian crandallite in dumortierite quartzites, Vaca Morta quarry, Vereda Range, Macaubas, Bahia, Brazil: Mineralogical Magazine, vol. 61, issue 4.

Wise, W.S., 1975, Solid solution between the alunite, woodhouseite, and crandallite mineral series: Neues Jahrbuch fiir Mineralogie Monatshefte.