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[RayStraw]

Chemical alteration of dark blue azurite crystals to bright green Malachite that exhibits the preservation of the original azurite surfaces—thus a pseudomorph.

In a recent paper (Rocks and Minerals vol 97 January/February 2022, pages 72-82) Southwood and Cairncross believe that “Alteration commences via a point of weakness on the surface of an azurite crystal, possibly at the site of a cleavage intersection, a point of contact, a fracture, or other imperfection.”

In a much earlier paper.Southwood and Cairncross indicate that inside the altering crystal, the reaction interface between the invading malachite and the residual azurite is commonly botryoidal, or “roughly concentric normal to the fibers” in the words of Palache and Lewis (American Mineralogist, 1927, p. 133).

Spherical, botryoidal primary malachite when broken through the center exhibits layered structure starting with a tiny sphere—Figure 1, Sepon Mine, Savannakhet Province, Laos, Ray Straw specimen and photo (2.2 cm diameter broken crystal).
An azurite crystal shows the botryoidal growth starting at the surface consistent with the Southwood and Cairncross as well as Palache and Lewis observations—Figure 2, Azurite altering to Malachite, Tsumeb Mine, Otavi Highlands, Namibia, Ray Straw specimen and Jeff Scovil photograph (4 x 2 x 1 cm crystal).

Does anyone have any other examples from any worldwide locations exhibiting surface initiated pseudomorphs as shown in Figure 2?

Thanks for looking!!!
Ray