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Azurite to Malachite pseudomorphs
  
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RayStraw




Joined: 21 Jul 2018
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Location: Bloomington Illinois

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PostPosted: Feb 26, 2023 17:50    Post subject: Azurite to Malachite pseudomorphs  

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



brokenbotyroidalRay.JPG
 Mineral: Malachite
 Locality:
Sepon Mine, Vilabouly District, Savannakhét Province, Laos (Lao P.D.R.)
 Dimensions: 2.2 cm sphere
 Description:
 Viewed:  9963 Time(s)

brokenbotyroidalRay.JPG



2023-02-0049surfnuclJS.jpg
 Mineral: azurite
 Locality:
Tsumeb Mine, Tsumeb, Otjikoto Region, Namibia
 Dimensions: 4 cm x 2 cm 1 cm crystal
 Description:
 Viewed:  9976 Time(s)

2023-02-0049surfnuclJS.jpg


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