Plumbogummite replacing Pyromorphite

specimen number:
8311516

location:
Laohuan Mine, Gongcheng Co., Guilin, Guangxi, China

description:
Prismatic crystals of what were once pyromorphite to 1.4 cm in size aesthetic across the top of matrix and in the process of being replaced by plumbogummite. This is a floater with no points of attachment and crystallized completely all around as seen in the video.

A pseudomorph, which literally translates from Greek as false form, is a mineral specimen that has chemically or structurally replaced another mineral while perfectly retaining the outward crystal shape of the original inhabitant. In the classic case of plumbogummite after pyromorphite, this process occurs in the highly oxidized zones of lead-bearing ore deposits where low-temperature, phosphate-rich meteoric waters interact with pre-existing, well-formed hexagonal prisms of pyromorphite. Over long periods of geological time, the original lead chlorophosphate (pyromorphite) is systematically dissolved and replaced by plumbogummite, a rare secondary lead-aluminum phosphate mineral. Because the replacement often occurs as a gradual, molecule-by-molecule substitution or as a dense encrustation that completely fills the mold of the dissolving host, the resulting specimen appears as a sharp, hexagonal pyromorphite crystal on the outside but consists entirely of microcrystalline or botryoidal plumbogummite, often boasting a vibrant sky-blue, green, or yellow color. These spectacular structural transformations are highly prized by collectors for their striking aesthetics and serve as precise geochemical indicators for researchers tracking the post-depositional alteration and fluid history of complex polymetallic vein systems.

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