Plumbogummite

plumbogummite

mimetite

crandallite

duftite

Images

Formula: PbAl₃(PO₄)(PO₃OH)(OH)₆
Hydrated phosphate containing hydroxyl, plumbogummite group, alunite supergroup
Crystal System: Trigonal
Specific gravity: 4.01
Hardness: 4½ to 5
Streak: White
Colour: Light blue, grey-white, yellow-grey, yellow, yellow-brown, red-brown, greenish, bluish, dark blue-grey
Solubility: Soluble in hot acids
Environments:

Hydrothermal environments

Plumbogummite is a relatively common secondary mineral in the oxidised zone of lead deposits (HOM) often associated with pyromorphite and baryte, as well as mimetite, duftite, cerussite, anglesite and wulfenite (HOM), and may be pseudomorphic after pyromorphite (common) or baryte .

Localities

At the Kintore Open Cut, New South Wales, Australia, plumbogummite occurs as a replacement of fluorapatite grains in a quartz-fluorapatite rock. It is also found at this locality as veins enclosing hinsdalite, in garnet sandstone (AJM 3.1.50).

At the New Cobar mine, New South Wales, Australia, plumbogummite occurs as small veinlets associated with malachite, azurite, cuprite and hematite (AJM 11.2.78).

The Laohuan "mine", Laohu, Gongcheng county, Guilin, Guangxi, China, is a collection of artisanal adits and excavations dug into the side of Laohu Hill, and originally worked for lead, zinc, silver and baryte, but commercial ore mining there ceased long ago.
Laohuan is the world’s most important locality for plumbogummite. At the 2012 Tucson Show, several dealers carried freshly collected lots of plumbogummite on yellow mimetite/pyromorphite from this locality. At the 2014 Ste.-Marie-aux-Mines show, several dealers had larger and better specimens of plumbogummite over mimetite/pyromorphite, with underlying crystals to 5 cm, some of these being total pseudomorphic replacements by plumbogummite. The 2014 Denver Show saw the first public displays of enormous, spectacular specimens of the plumbogummite pseudomorphs after pyromorphite, the grey-green to sky-blue plumbogummite ranging from thin coatings over the pyromorphite crystals to total replacements, in clusters to 16 cm across. The forms of the deeply hoppered original pyromorphite crystals are faithfully preserved; the individual pseudomorphic crystals reach 5.5 cm (Minrec 53.6.697-732).
The plumbogummite pseudomorphs after pyromorphite are sometimes very colourfully fluorescent, best observed under mid-wave UV (303 nm). The plumbogummite shows bright green fluorescence with bright orange accents provided by residual unaltered pyromorphite, seen mainly at some of the crystal tips. A similar response is seen under short wave UV (254 nm) but the orange pyromorphite response is more subdued burnt orange colour. Under long wave UV (365 nm) a bright, monochromatic, pale blue fluorescence is seen. The daylight colour is pale blue-green. The green fluorescence is probably activated by trace amounts of (UO₂)²⁺ (Minrec 54.4.364).

At Yangshuo, Guangxi, China, plumbogummite occurs with pyromorphite (AESS), and plumbogummite pseudomorphs after pyromorphite have been found (KL p210).

At the type locality, Huelgoat, Brittany, France, plumbogummite occurs in a polymetallic lead vein with pyromorphite, cerussite, anglesite and wulfenite (Dana, Mindat).

Plumbogummite from Huelgoat - Image

At Dry Gill mine, Caldbeck, Allerdale, Cumbria, UK, plumbogummite occurs on quartz with associated pyromorphite (AESS)

At Roughton Gill, Caldbeck, Allerdale, Cumbria, UK, plumbogummite occurs as encrustations on quartz or pyromorphite, occasionally overgrown by mottramite, and also associated with mimetite. It sometimes forms epimorphs after pyromorphite at this locality (JRS 11.20, Dana, MinRec 41.1.42).

At the Mexico mine, Roughton Gill, Allerdale, Cumbria, UK, plumbogummite is associated with pyromorphite (MinRec 41.1.34).

At Burdell Gill, Mungrisdale, Eden, Cumbria, UK, plumbogummite has been found encrusting goethite-coated quartz, associated with or replacing mimetite. It is also found as a coating on beudantite crystals at this locality (JRS 8(1).6).

At the Canton mine, Cherokee county, Georgia, USA, plumbogummite is associated with marcasite (Dana).

At the Upper dumps, North Star Mine, Mammoth, Tintic Mining District, Juab County, Utah, USA, plumbogummite has been found on quartz matrix associated with fluorapatite. One specimen of tan plumbogummite crystals that was analyzed showed an unusual amount of tellurium. No further analysis has been done, but this plumbogummite was found with a small black metallic fragment of goldfieldite in a vug in quartz (MinRec 55.2.218).

Plumbogummite from the Upper Dumps - Image

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