Plumbophyllite

plumbophyllite

plumbotsumite

sepiolite

chrysocolla

Images

Formula: Pb2Si4O10.H2O
Hydrated phyllosilicate (sheet silicate)
Crystal system: Orthorhombic
Specific gravity: 3.96 measured, 3.940 calculated for the empirical formula
Hardness: 5
Streak: White
Colour: Pale blue to very light blue-green
Luminescence: No fluorescence under UV
Solubility: Decomposes immediately (and dramatically) in cold, dilute hydrochloric acid with exfoliation and formation of a white precipitate of PbCl2 (cotunnite) (HOM).
Environments

Sedimentary environments
Metamorphic environments

Localities

At the type locality, the Blue Bell Mine, Zzyzx, Soda Mountains, Silver Lake Mining District, San Bernardino County, California, USA, as early as 1949, rich specimens of linarite, caledonite and leadhillite were known from the deposit. Collecting efforts have continued to yield unusual oxidation-zone assemblages of rare minerals; Some of the more significant recent (in 2009) discoveries have been kuksite, quetzalcoatlite and plumbotsumite.
Plumbophyllite is found in cracks and narrow veins in a highly siliceous quartzite-like hornfels in a fractured and chaotic region of limestone showing irregular skarn formation. These cracks appear to have been initially filled largely with cerussite, silica, and/or chrysocolla.
The plumbophyllite appears to be a tertiary mineral formed from the cerussite. Species observed in direct association with plumbophyllite include cerussite, chrysocolla, fluorite, goethite, gypsum, mimetite, opal, plumbotsumite, pyromorphite, quartz, sepiolite and wulfenite. Other species identified nearby include fluorapatite, beudantite, boleite, calcite, celestine, creaseyite, dioptase, ferrisurite, hemimorphite, mottramite, plumbogummite and vanadinite. The conditions of formation must have been relatively basic because plumbophyllite is unstable in even weakly acidic environments.
Plumbophyllite forms prismatic crystals with wedge-shaped terminations that typically occur in divergent sprays. Individual crystals are up to 3.0 × 0.3 × 0.2 mm3. Crystals are colourless to pale blue and transparent with vitreous lustre (AM 94.1198–1204).
Plumbophyllite from the Blue Bell Mine - Image

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