Conichalcite

Conichalcite
A thin crust of Conichalcite on a rock.
General
Category	Arsenate Minerals
Formula (repeating unit)	CaCu(AsO4)(OH)
Strunz classification	7/B.26-50
Dana classification	41.5.1.2
Crystal system	Orthorhombic
Unit cell	V 397.66 ų
Identification
Color	grass green to light green
Crystal habit	crusts of acicular to almost fibrous crystals. Also as botryoidal masses and compact crusts.
Twinning	rare
Cleavage	absent
Fracture	uneven
Tenacity	brittle
Mohs scale hardness	4.5
Luster	vitreous, greasy
Streak	green
Diaphaneity	translucent
Specific gravity	4.3
Density	4.33 g/cm3
Optical properties	biaxial (+/-)
Refractive index	nα = 1.778 - 1.800 nβ = 1.795 - 1.831 nγ = 1.801 - 1.846
Birefringence	δ = 0.023 - 0.046
Pleochroism	visible
Dispersion	Strong r < v to r < v moderate
Other characteristics	easily soluble in HCl or HNO3
References

Conichalcite, CaCu(AsO₄)(OH), is a relatively common arsenate mineral related to duftite (PbCu(AsO₄)(OH)), limonite, malachite, beudantite, adamite, cuproadamite, olivenite and smithsonite. It is green, often botryoidal, and occurs in the oxidation zone of some metal deposits. Notable occurrences of conichalcite include Juab Co., Utah, Nevada and Arizona, the USA; Mexico; Chile; Poland and Zaire.

Physical Characteristics

Color: is grass green to light green. Lustre: is vitreous. Transparency: is transparent to translucent. Crystal System: is orthorhombic. Crystal habit: include the crusts of acicular to almost fibrous crystals. Also as botryoidal masses and compact crusts. Cleavage: is absent. Fracture: is uneven. Hardness: is 4.5. Specific Gravity is approximately 4.3. Streak is green.

The best field indicators of conichalcite are its crystal habit, color, associations and density.

Formation

Conichalcite forms in large copper ore bodies. Here, in what are known as oxidation zones, ground water enriched with oxygen react with copper sulfide and copper oxide to produce a dazzling array of colorful minerals such as malachite, azurite and [linnarite]]. Conichalcite is just one of the many minerals that form in oxidation zones. Conichalcite is often found encrusted on to limonitic rocks that have yellow to red colors. These combined with the verdant green of the mineral often make for vibrant specimens.

Conichalcite will also form a solid solution series with the mineral calciovolborthite. When these two minerals form a solid solution series, the two interchanging elements are arsenic and vanadium. Conichalcite is the arsenic rich end member of the series and calciovolborthite is the vanadium rich end member.