Earth Record
Mineralogy and formation
Shattuckite with chrysocolla is a combination of two secondary copper silicate minerals that form together in the oxidation zones of copper ore deposits. Shattuckite (Cu₅(SiO₃)₄(OH)₂) is a relatively rare copper silicate that crystallizes in the orthorhombic system, forming acicular to fibrous crystals with an intense deep blue color. Chrysocolla ((Cu,Al)₂H₂Si₂O₅(OH)₄·nH₂O) is an amorphous to cryptocrystalline hydrated copper silicate with a characteristic blue-green to turquoise color.
Both minerals form when copper-bearing primary sulfides (chalcopyrite, chalcocite, bornite) weather in the presence of silica-rich groundwater. The oxidation process releases copper ions that react with dissolved silica under different pH and concentration conditions to produce these distinct minerals, often in intimate association. The deeper blue of shattuckite against the lighter blue-green chrysocolla creates visually striking specimens.
The type locality for shattuckite is the Shattuck Mine in Bisbee, Arizona. Other significant sources include Namibia (the Kaokoveld), the Democratic Republic of Congo, and Greece.
Chemical FormulaShattuckite: Cu5(SiO3)4(OH)2 (copper inosilicate/chain silicate) occurring with chrysocolla: (Cu,Al)2H2Si2O5(OH)4 nH2O (hydrated copper aluminum silicate, amorphous to cryptocrystalline); often additionally intermixed with quartz (SiO2), malachite Cu2(CO3)(OH)2, azurite Cu3(CO3)2(OH)2, and/or dioptase CuSiO3 H2OCrystal SystemMixedMohs Hardness3.5Specific GravityShattuckite: 3.8--4.1; Chrysocolla: 2.0--2.4; combined specimens variable depending on ratioLusterShattuckite: vitreous to silky (fibrous habit common); Chrysocolla: vitreous to waxy to earthy; combination specimens typically show complex mixed luster with silky blue shattuckite zones within waxy chrysocolla matrixColorBlue-GreenIMA StatusrockIMA NumberGrandfathered (pre-1959) NamibiaUSA (Arizona)
Telling it apart
The fraud risk here is oversimplification. Sellers often label any mixed blue copper stone as either pure shattuckite or pure chrysocolla when the specimen is actually an association of several secondary minerals. In a true shattuckite with chrysocolla piece, the darker royal blue zones belong to the denser, more crystalline shattuckite, while the softer blue green areas usually reflect chrysocolla.
Quartz, malachite, or azurite may also be present, so the label should describe a mix, not pretend to laboratory purity. Chrysocolla rich material is softer and less structurally ordered. Shattuckite rich material usually carries more collector interest. Buyers should look for clear color contrast, truthful locality information, and acknowledgment that the specimen is composite. When a seller admits the association, the stone becomes more interesting, not less.
The geology is the value here.
A careful buyer should compare the label to habit, hardness, and provenance before paying a rarity premium. This combination should show two distinct copper silicate phases — shattuckite is orthorhombic and fibrous while chrysocolla is amorphous and waxy. If the piece looks uniform throughout, one phase may be absent.
Spotting the real thing
Shattuckite with chrysocolla: two copper minerals naturally intergrown. Shattuckite (darker blue, Mohs 3. 5, fibrous habit) and chrysocolla (softer blue-green, Mohs 2-4).
Both should be copper-blue tones but distinguishable. If the specimen shows only one shade of blue-green with no textural variation, it may be single-mineral rather than a genuine intergrowth.
Cross-referenceMindat ↗