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Formula: PbFe3+3(AsO4)(AsO3OH)(OH)6
Hydrated arsenate containing hydroxyl,
dussertite group, forms a series with
beudantite
Specific gravity: >4.2
Hardness: 4
Streak: Pale yellow
Colour: Greenish to yellowish-brown
Environments:
Segnitite is an arsenic-bearing mineral.
Localities
At the Kintore pit, New South Wales, Australia, segnitite is found in the oxidised zone of
lead-zinc sulphide ore bodies
where it overgrows beudantite on a matrix of
goethite encrusting quartz and
small spessartine crystals. It is also associated with
mimetite, carminite,
bayldonite, agardite-Y and
mawbyite
(Dana).
In the Slitt Vein at Heights Pasture Mine, Weardale, County Durham, England, UK, segnitite has been found in the
supergene weathering zone in manganese oxide-rich pockets and as crusts on
quartz. The mine worked a substantial fluorite orebody
both underground and in a large surface excavation, and it is from this surface working that the segnitite was recovered.
The Slitt vein here cuts limestone and the overlying
sandstone and shale, and is composed
almost entirely of quartz with wide lenses of
fluorite. Galena occurs in very small amounts disseminated
within the quartz and fluorite. The segnitite
is clearly of supergene origin
(JRS 19.39-42).
At Roughton Gill, Cumbria, segnitite occurs with carminite and
beudantite in fractures in
quartz-rich rock
(JRS 11.22).
At the San Rafael Mine, Nevada, segnitite occurs as a crystalline aggregate in pods of oxidised
galena and anglesite with
kaolinite and covellite. In
the altered rock bordering the pods segnitite occurs with
scorodite, carminite and
mimetite, and with adamite in
pods of limonite
gossan.
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