Linarite is a rare secondary mineral, chemical formula PbCu(SO4)(OH)2, occurring in the oxidation zones of lead and copper sulphide deposits. It is named for the Linares mining district in southern Spain where the species was first described, and it crystallises in the monoclinic system, typically as deep ultramarine to azure-blue prismatic crystals or as crystalline crusts and aggregates. Linarite is exclusively a collector's mineral; its hardness of 2.5 on the Mohs scale and its perfect cleavage in two directions make it entirely unsuited to jewellery use.

Physical and optical properties

Linarite has a specific gravity of approximately 5.3 to 5.5, reflecting its high lead content. Refractive indices are 1.809 to 1.859, with a birefringence of 0.050 (high for any gem-class mineral). The colour is consistently deep blue, often described as ultramarine, with no significant pleochroism observed in most material. Lustre is vitreous to subadamantine. Streak is pale blue. Crystals are typically prismatic, often as elongated tabular forms with striated faces, and rarely exceed a few millimetres in length, though exceptional specimens from the Mammoth-Saint Anthony Mine in Arizona have produced individual crystals over 2 centimetres long.

Localities

Linarite occurs sparingly at lead-copper deposits worldwide. The original locality at Linares, Spain, has produced fine reference material since the nineteenth century. Other significant localities include Tsumeb, Namibia (one of the principal sources for collector specimens); Mammoth-Saint Anthony Mine, Pinal County, Arizona; the Sunshine and Grand Reef Mines in Arizona; Caldbeck Fells, Cumbria, England; and Roughten Gill, also in Cumbria. Australian and Mexican occurrences contribute additional collector material.

Identification

Linarite is most easily confused with azurite (Cu3(CO3)2(OH)2), which has a similar deep blue colour but lower density and effervesces in dilute acid (linarite does not). Linarite's high specific gravity (resulting from the lead content) is a reliable separator: a fragment dropped into bromoform (specific gravity 2.89) sinks rapidly, distinguishing it from azurite (specific gravity 3.77 to 3.78) only by careful comparison, but heavy liquids of higher density readily separate the two. Refractive index measurement, where the soft crystals permit, is also definitive.

Collector market

Quality linarite specimens, particularly Tsumeb and Mammoth-Saint Anthony material, command meaningful prices at major mineral shows. Crystallised material with sharp prismatic habits and undamaged terminations from these localities can reach the low to mid four-figure range for thumbnail and miniature specimens. The mineral is not lapidaried; its softness, cleavage, and low resistance to atmospheric chemical attack rule out cabbing or facetting in any practical sense.