Caledonite

Mineral

Not to be confused with Celadonite.

Caledonite
Caledonite (green) on cerussite
General
Category	Sulfate minerals
Formula (repeating unit)	Cu₂Pb₅(OH)₆CO₃(SO₄)₃
IMA symbol	Cdo^[1]
Strunz classification	7.BC.50
Crystal system	Orthorhombic
Crystal class	Pyramidal (mm2) (same H-M symbol)
Space group	Pmn2₁
Unit cell	a = 20.089(7) Å, b = 7.146(3) Å, c = 6.56 Å; Z = 2
Identification
Color	Blue; green
Crystal habit	Typically striated prismatic or tabular crystals; radial aggregates
Cleavage	[001] perfect; [100] distinct
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	2.5–3
Luster	Vitreous
Streak	Green-white; blue-green
Diaphaneity	Transparent to translucent
Specific gravity	5.6–5.8
Optical properties	Biaxial (−)
Refractive index	n_α = 1.818(3) n_β = 1.866(3) n_γ = 1.909(3)
Birefringence	δ = 0.091
Pleochroism	Weak
2V angle	Measured: 85°
References	^[2]^[3]^[4]^[5]

Caledonite, whose name derives from Caledonia, the historical name of its place of discovery (Scotland), is a richly colored blue-green sulfate-carbonate mineral of lead and copper with an orthorhombic crystal structure. It is an uncommon mineral found in the oxidized zones of copper-lead deposits.

Collectible properties

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Caledonite's primary use is a collector's mineral. Although it contains copper and lead, it is a secondary mineral and is not prevalent enough in any known deposits to be used as an ore. Caledonite, when developed into full crystals, can have a deep blue-green color reminiscent of secondary copper minerals. Its high lustre, on the other hand, is more like secondary lead minerals. Localities in which caledonite occurs as well developed crystals are quite rare and include the Mammoth-St. Anthony Mine at Tiger, Arizona, a few mines in California, such as the Reward Mine. A few other mines in Arizona and Chile have been known to produce samples.

Associated minerals

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Given that caledonite is found in oxidized copper/lead deposits, it is frequently found in association with other copper and lead minerals. Frequently associated minerals include: linarite, malachite, cerussite, brochantite, anglesite, leadhillite, and azurite.^[3]

Notes for identification

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Caledonite's blue color is a useful indicator, but insufficient, especially since one of its associates, linarite, is a vivid blue as well. Useful tests for determining if a specimen is caledonite include its density, streak, and crystal habit.