Segnitite

Segnitite
Segnitite with lepidocrocite from the Alto das Quelhas do Gestoso Mines, Gestoso, Manhouce, São Pedro do Sul, Viseu District, Portugal. Picture width 1 mm. Yellow brown segnitite with red brown lepidocrocite.
General
Category	Arsenate minerals
Formula (repeating unit)	Lead iron(III) arsenate, PbFe3H(AsO4)2(OH)6
IMA symbol	Sgt[1]
Strunz classification	7/B.36-165
Dana classification	42.7.4.4
Crystal system	Trigonal
Crystal class	Hexagonal scalenohedral – 3m (32/m)
Space group	R3m
Unit cell	a = 7.359(3) Å, c = 17.113(8) Å, V = 802.6(6) Å3+, Z = 6
Identification
Color	Greenish brown to yellowish brown and dark brown
Crystal habit	Tabular, rhombohedral, pseudo-octahedral, pseudo-cubic and very rarely also acicular crystals.
Twinning	Not well observed
Cleavage	Distinct on {001}
Fracture	Rough, irregular, uneven
Tenacity	Brittle
Mohs scale hardness	4
Luster	Adamantine to vitreous
Streak	Pale yellow
Diaphaneity	Transparent to translucent
Specific gravity	4.2
Optical properties	Uniaxial (−), e=1.955, w=1.975
Refractive index	nω = 1.955 to 1.975, nε = 1.975
Birefringence	δ = 0.020
Pleochroism	Pale to moderate yellow
References	[2][3][4][5]

Segnitite is a lead iron(III) arsenate mineral. Segnitite was first found in the Broken Hill ore deposit in Broken Hill, New South Wales, Australia. In 1991, segnitite was approved as a new mineral. Segnitite has since been found worldwide near similar locality types where rocks are rich in zinc and lead especially. it was named for Australian mineralogist, gemologist and petrologist Edgar Ralph Segnit. The mineral was named after E. R. Segnit due to his contributions to Australian mineralogy.^[4]

Segnitite is not a primary ore mineral, but is found amongst other well known ore minerals such as galena, sphalerite, pyrite and more. Many minerals found with segnitite are important for industrial purposes. Minerals associated with segnitite make up metal alloys, batteries and even pigments. Carminite and beudanite are closely related to segnitite. In fact, forms of beudanite are commonly confused with segnitite, as the sulfate and arsenate anions are readily exchangeable with each other. Other mineral relations include, goethite, coronadite, agardite, bayldonite, and mimetite.^[4]

Set parameters for the space group and chemical composition have yet to be confirmed. Segnitite has loose boundaries and conclusions about segnitite were derived from associated minerals. Chemically, there are many varieties of segnitite which affects space group measurements and chemical analysis interpretations. In other words, segnitite samples from around the world can be very different from one another making it difficult to provide accurate chemical measurements.^{[citation needed]}