On pseudomalachite and cornetite

L. G. Berry

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Research Article| June 01, 1950

On pseudomalachite and cornetite

L. G. Berry

Queen's University, Kingston, Ontario, Canada

* Associate Professor, Department of Mineralogy.

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Author and Article Information

L. G. Berry

Queen's University, Kingston, Ontario, Canada

* Associate Professor, Department of Mineralogy.

Publisher: Mineralogical Society of America

First Online: 06 Jul 2018

Online ISSN: 1945-3027

Print ISSN: 0003-004X

Mineralogical Society of America

American Mineralogist (1950) 35 (5-6): 365–385.

Abstract

New observations combined with existing chemical analyses on pseudomalachite and cornetite from several localities lead to the following description of the two minerals.

Pseudomalachite is monoclinic, prismatic, with space group P2_i/a; the unit cell with a=17.06, b=5.76, c=4.49A, β=91°02′ a:b:c=2.962:1:0.7795 contains Cu₁₀(PO₄)₄(OH)₈ = 2[Cu₅(PO₄)₂(0H₄)]; calculated specific gravity 4.34. Cleavage (100) perfect and difficult. Specific gravity 4.30-4.35 (coarse crystalline material), 4.08-4.21 (radiating and cryptocrystalline materials). Many specimens labelled pseudomalachite, dihydrite, ehlite, lunnite, tagilite, phosphorochalcite and prasine give the x-ray powder pattern of pseudomalachite.

Cornetite is orthorhombic, dipyramidal, with space group Pbca; the unit cell with a=10.88, b = 14.10, c = 7.11A, a:b:c=0.772:1:0.504. contains Cu₂₄(PO₄)₈(OH)₂₄ = 8[Cu₃PO₄(OH)₃]; calculated specific gravity 4.10. Crystals commonly dipyramidal, showing forms d(210), v(121), n(021), p(221) with (021):(021)=90°33′ (calc.) No cleavage observed. Specific gravity 4.10 (Hutchinson & MacGregor). Ungemach's elements (1929) transformed to the structural setting by 001/200/010 become 0.7715:1:0.5048.