Formula: PbFe3+3(AsO4)(AsO3OH)(OH)6
Hydrated arsenate containing hydroxyl, forms a series with beudantite
Specific gravity: >4.2
Hardness: 4
Streak: Pale yellow
Colour: Greenish to yellowish-brown

Hydrothermal environments

Segnitite is an arsenic-bearing mineral.


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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