Cyclosilicate (ring silicate), margarosanite group
Specific gravity: 4.33
Hardness: 2½ to 3
Colour: Colourless or greyish-white due to included native lead
Solubility: Decomposes in nitric acid with separation of silica (Dana)
Common impurities: Fe,Zn,Mg,Ba,H2O
Margarosanite is a rare lead silicate found in metamorphosed
At the Långban mine, Långban Ore District, Filipstad, Värmland County, Sweden, margarosanite has been reported in association with nasonite, diopside variety schefferite, apophyllite, calcite and thaumasite (AM 48.698-703).
At the type locality, the Parker shaft, Franklin Mine, Franklin, Franklin Mining District, Sussex County, New Jersey, USA, margarosanite occurs in a metamorphosed stratiform zinc deposit associated with nasonite, minehillite, almandine, hancockite, roeblingite, franklinite, willemite, rhodonite, axinite-(Mn), datolite, prehnite, manganoan biotite, johannsenite, baryte, wollastonite, vesuvianite, microcline, lead, grossular, clinohedrite, bustamite and andradite (AM 1.87-88, HOM, Mindat).
Paragenesis of Margarosanite at the type locality
Margarosanite's apparent scarcity is related to its deposition at moderately high temperatures. It has been synthesised at 350oC.
The implied paragenesis is hardystonite → larsenite → esperite → margarosanite. The association with additional lead and lead-zinc silicates such as barysilite, clinohedrite, hancockite, nasonite and roeblingite may be localised. Co-occurring minerals include andradite, axinite-(Mn), baryte, bustamite, franklinite, grossular and its variety caswellite, hodgkinsonite, native lead, feldspars (microcline and its variety hyalophane, celsian), minehillite, pectolite, prehnite, vesuvianite, grossular variety cyprine, willemite, xonotlite and wollastonite.
Overlap in crystallisation is the rule.
The early minerals (hardystonite, feldspars, wollastonite, andradite, franklinite, and rarely bustamite) formed at relatively high temperatures. Garnets are stable across a wide temperature range. Toward lower temperatures, hydrated species were stable and were part of the end alteration of the primary minerals, often as fine-grained masses (R&M 90.6.573-574).
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