"Rock of the Month # 294, posted for December 2025" ---

Purpurite, a rare phosphate mineral

Composed of common elements (Mn, P and O) this phosphate is nevertheless an unusual material, seldom found. Purpurite is orthorhombic in crystal form, but often in fine-grained crusts and aggregates, as here, formula Mn³⁺PO₄. It is a secondary mineral developed late in the evolution of granitic pegmatites, which may display a bewildering range of primary and secondary phosphate minerals (Simmons et al., 2022, pp.146-179). It is the Mn analogue of heterosite, Fe³⁺PO₄. At the Varutrask lithium pegmatite in Sweden, the phosphate lithiophilite is a rare primary phase, and may have oxidation rims of sicklerite and purpurite (Quensel and Berggren, 1940). Similar assemblages occur at the Stewart pegmatite in the Pala district of southern California (Shigley and Brown, 1985). Under the microscope, purpurite displays intense pleochroism and high relief (Melgarejo and Martin, 2011, p.335). It is associated with primary phosphates, and with lithium minerals such as lepidolite and spodumene. As an attractive stone it is of interest to the lapidary trade, though it is not particularly hard (Mohs hardness 4 to 4.5: Thomas, 2008, p.130).

Bernard and Hyrsl (2015, p.554) list some prominent localities for purpurite, including the the Boca Rica mine near Sapucaia da Norte in Minas Gerais, a likely source of this month's specimen. The Sapucaia pegmatite in Minas Gerais, a complex body with five zones, is noted for complex phosphate assemblages (including heterosite: Cassedanne and Baptista, 1999; Baijot et al., 2012). The area is east of Governador Valadares (see also Menezes, 2009: the Sapo pegmatite, one of the many mines in the district, has produced huge quartz crystals and superb apatite crystal clusters). Other sites (Bernard and Hyrsl, 2015) include localities in Connecticut, North Carolina, South Dakota and California, as well as occurrences in France, Rwanda, Namibia and Western Australia. Purpurite is also found at the Emmons quarry in Oxford county, Maine (noted in a museum collection: MMGM, 2022, see also Rand, 1957). The type locality is the Faires mine, Kings Mountain, Cleveland county, N.Carolina.

REFERENCES

Baijot,M, Hatert,F and Philippo,S (2012) Mineralogy and geochemistry of phosphates and silicates in the Sapucaia pegmatite, Minas Gerais, Brazil: genetic implications. Can.Mineral. 50, 1531-1554.

Bernard,JH and Hyrsl,J (2015) Minerals and their Localities. Granite, Prague, Czech Republic / Mineralogical Record Bookstore, Tucson, 3rd edition, 920pp.

Cassedanne,JP and Baptista,A (1999) The Sapucaia pegmatite, Minas Gerais, Brazil. Mineral.Record 30 no.5, 347-360.

London,D (2008) Pegmatites. Canadian Mineralogist Spec.Publ. 10, 347pp. + CD-ROM.

Melgarejo,JC and Martin,RF (2011) Atlas of Non-Silicate Minerals in Thin Section. Canadian Mineralogist Spec.Publ. 7, 522pp. plus CD-ROM.

Menezes,L (2009) The Sapo mine, Ferruginha district, Conselheiro Pena, Minas Gerais, Brazil. Mineral.Record 40, 273-292.

MMGM (2022) Maine Mineral & Gem Museum. MMGM, 99 Main Street, Bethel, ME, tour (07 September 2022).

Quensel,P and Berggren,T (1940) Minerals of the Varutrask Pegmatite 16: lithiophilite, a third primary alkali-manganese phosphate from Varutrask. GFF 62, 291-296.

Rand,JR (1957) Maine pegmatite mines and prospects and associated minerals. Maine Geological Survey Mineral Resources Index 1, reprinted 1973, 43pp.

Shigley,JE and Brown,GE (1985) Occurrence and alteration of phosphate minerals at the Stewart pegmatite, Pala District, San Diego County, California. Amer.Mineral. 70, 395-408.

Simmons,W, Webber,KL, Falster,AU, Roda-Robles,E and Dallaire,DA (2022) Pegmatology. Pegmatite Mineralogy, Petrology and Petrogenesis. 2nd edition. Rubellite Press, Cana, VA, 287pp.

Thomas,A (2008) Gemstones: Properties, Identification and Use.New Holland Publishers (UK) Ltd, 256pp.