Connellite

Connellite is a rare mineral species, a hydrous copper chloro-sulfate,[5] Cu₁₉(OH)₃₂(SO₄)Cl₄·3H₂O, crystallizing in the hexagonal system. It occurs as tufts of very delicate acicular crystals of a fine blue color, and is associated with other copper minerals of secondary origin, such as cuprite and malachite. Its occurrence in Cornwall, England, was noted by Philip Rashleigh in 1802, and it was first examined chemically by Prof Arthur Connell FRSE in 1847, after whom it is named.[5]

Connellite
General
Category	Halide mineral
Formula (repeating unit)	Cu19(OH)32(SO4)Cl4·3H2O
Strunz classification	3.DA.25
Crystal system	Hexagonal
Crystal class	Dihexagonal dipyramidal (6/mmm) H-M symbol: (6/m 2/m 2/m)
Space group	P63/mmc
Unit cell	a = 15.78 Å, c = 9.10 Å; Z = 1
Identification
Color	Azure blue, blue green
Crystal habit	Clusters of divergent acicular crystals, fibrous, crusts
Cleavage	None
Fracture	Splintery
Tenacity	Brittle
Mohs scale hardness	3
Luster	Vitreous
Streak	Pale green-blue
Diaphaneity	Translucent
Specific gravity	3.36 to 3.41
Optical properties	Uniaxial (+)
Refractive index	nω = 1.724 - 1.746 nε = 1.738 - 1.758
Birefringence	δ = 0.014
References	[1][2][3][4]

The type locality is Wheal Providence at Carbis Bay in Cornwall.[3] Outside Cornwall it has been found in over 200 locations worldwide including Namaqualand in South Africa and at Bisbee, Arizona (US).[3]

Connellite crystal structure: Color code: Cu: copper, S: olive, O: red, Cl: green; Cell: magenta

References

1. https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Connellite Mineralienatlas
2. Connellite in the Handbook of Mineralogy
3. Connellite: Connellite mineral information on Mindat.org
4. Connellite data on Webmineral
5.  One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Connellite". Encyclopædia Britannica. 6 (11th ed.). Cambridge University Press. p. 963.