Chalcanthite

Chalcanthite
General
Category	Sulfate minerals
Chemical formula	CuSO4·5H2O
Strunz classification	07.CB.20
Crystal symmetry	Triclinic 1 pinacoidal
Unit cell	a = 6.11 Å, b = 10.673 Å, c = 5.95 Å; α = 97.58°, β = 107.17°, γ = 77.55°; Z = 2
Identification
Color	Berlin blue to sky-blue, greenish blue
Crystal habit	Typically stalactitic, encrusted, reniform or massive. Natural crystals are rare, but are short prismatic or tabular
Crystal system	Triclinic
Twinning	Rare as cruciform twins
Cleavage	Perfect on {110}; interrupted on {110}
Fracture	Conchoidal
Mohs scale hardness	2.5
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.12 - 2.3
Optical properties	Biaxial (-)
Refractive index	nα = 1.514 nβ = 1.537 nγ = 1.543
Birefringence	δ = 0.029
Solubility	Soluble in water, turning it blue
Other characteristics	Poisonous
References	[1][2][3]

Chalcanthite, whose name derives from the Greek, chalkos and anthos, meaning copper flower, is a richly-colored blue/green water-soluble sulfate mineral CuSO₄·5H₂O. It is commonly found in the late-stage oxidation zones of copper deposits. Due to its ready solubility, chalcanthite is more common in arid regions.

Chalcanthite is a pentahydrate and the most common member of a group of similar hydrated sulfates, the chalcanthite group. These other sulfates are identical in chemical composition to chalcanthite, with the exception of replacement of the copper ion by either manganese as jokokuite, iron as siderotil, or magnesium as pentahydrite.^[4]

Uses of chalcanthite

Chalcanthite on limonite from Washington Camp, Santa Cruz County, Arizona (size: 5.5 x 2.9 x 1.5 cm)

As chalcanthite is a copper mineral, it can be used as an ore of copper. However, its ready solubility in water means that it tends to crystallize, dissolve, and recrystallize as crusts over any mine surface in more humid regions. Therefore, chalcanthite is only found in the most arid regions in sufficiently large quantities for use as an ore.

Secondarily, chalcanthite, due to its rich color and beautiful crystals, is a sought after collector's mineral. However, as with its viability as an ore, the solubility of the mineral causes significant problems. First, the mineral readily absorbs and releases its water content, which, over time, leads to a disintegration of the crystal structure, destroying even the finest specimens. It is critical to store specimens properly to limit exposure to humidity. Second, higher quality crystals can be easily grown synthetically, and, as such, there is a concern that disreputable mineral dealers would present a sample as natural when it is not.

Associated minerals

Given that chalcanthite is found in oxidized copper deposits, it is frequently found in association with other copper minerals. Frequently associated minerals include

• Calcite and its polymorph, aragonite, both CaCO₃
• Brochantite, Cu₄(SO₄)(OH)₆
• Chalcopyrite, CuFeS₂
• Malachite, Cu₂(CO₃)(OH)₂
• Melanterite, FeSO₄ · 7H₂O

Alternative names

Chalcanthite has several alternative names, including blue stone, blue vitriol, and copper vitriol.

Notes for identification

Chalcanthite's blue color is one of its most notable features, but it is insufficient in identification. Other useful tests include associated minerals, crystal habit, solubility and subsequent coloring of the water blue, and taste. A special note on tasting chalcanthite, however: chalcanthite has a sweetly metallic taste, but taste testing should not be done haphazardly. The specimen should be never touched with the tongue, as chalcanthite is poisonous. The liquid from chalcanthite will also stain skin blue for several days.

See also

• Copper(II) sulfate

References

1. ^ Webmineral listing
2. ^ MinDat listing
3. ^ Handbook of Mineralogy
4. ^ Mindat Chalcanthite group

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