Kaňkite

Kankite
Kankite
	Kaňkite found in the Czech Republic
General
Category	Arsenate mineral
Formula; (repeating unit)	Fe3+AsO4·3.5(H2O)
IMA symbol	Kňk
Strunz classification	8.CE.60
Crystal system	Monoclinic ; Unknown space group
Unit cell	a = 18.803(15), b = 17.490(18) ; c = 7.633(5) [Å]; β = 92.72°; z = 16
Identification
Formula mass	257.82 g/mol
Color	Yellowish–green
Crystal habit	Tabular spearlike crystals in spherulites and botryoidal encrustations
Fracture	Uneven
Mohs scale hardness	2–3
Luster	Dull to vitreous
Streak	Grayish yellow
Diaphaneity	Translucent
Specific gravity	2.60 – 2.70
Optical properties	Biaxial
Refractive index	nα = 1.664 nγ = 1.680
References

Kankite is a mineral with the chemical formula Fe³⁺As O₄·3.5(H₂O). Kankite is named for the locality that yielded first specimens Kaňk, Czech Republic.^[2] Kankite forms in old (1200- to 1400-year-old) mine dumps.^[3] It is yellowish-green on fresh exposure, with a paler greenish yellow on exposure to air.

Properties

Kankite is a monoclinic mineral, meaning it is a mineral system having 3 unequal axes of which one is at right angles with the other two. It has an uneven fracture and has a hardness of 2–3 (gypsum–calcite). It is translucent yellowish green in color with a grayish-yellow streak. Its luster is dull to vitreous. Kankite contains the elements arsenic, iron, hydrogen and oxygen.^[4] It was approved by the IMA in 1976. Its habit is botryoidal, "grape-like" rounded forms (e.g. malachite). It forms encrustations, crust-like aggregates on matrix. The specific gravity of Kankite is 2.70.^[3]

Occurrences

Kankite was first described in 1976 for an occurrence in the Kaňk, Kutná Hora, Bohemia, Czech Republic.^[5] It is a rare secondary mineral in highly weathered mine dumps containing arsenopyrite (in the Czech Republic). It occurs in association with scorodite, pitticite, parascorodite, zykaite, arsenopyrite, vajdakite, native arsenic, pyrite, proustite, gypsum, “limonite” and quartz.^[2]

It has also been reported from Munzig near Meissen; from Brand-Erbisdorf, Saxony; from Menzenschwand, Black Forest in Germany. It occurs at King's Wood mine, Buckfastleigh, Devon, and from the South Terras mine, St. Stephen-in-Brannel, Cornwall in England. It has also been reported from the Suzukura mine north-northeast of Enzan, Yamanashi Prefecture, Japan.^[2]

References

^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
^ ^a ^b ^c ^d Handbook of Mineralogy
^ ^a ^b ^c Webmineral data
^ ^a ^b [1], Frost, Ray L. and Cejka, Jin and Keeffe, Eloise C. and Sejkora, Jiri (2009)Raman Spectroscopic study of the mixed anion sulphate-arsenate mineral pamnauiteJournal of Raman Spectroscopy, 40(11) pp. 1547–1550.
^ ^a ^b Mindat.org