Cerchiaraite-(Mn)

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Formula: Ba₄Mn³⁺₄(Si₄O₁₂)O₂(OH)₄Cl₂[Si₂O₃(OH)₄]
Cyclosilicate (ring silicate), cerchiaraite group, barium- and manganese- bearing mineral
Crystal System: Tetragonal
Specific gravity: 3.62 measured, 3.70 calculated for the empirical formula
Hardness: 4 to 5
Streak: Pale green
Colour: Deep green
Luminescence: Not fluorescent
Environments

Metamorphic environments

Localities

At Woods Mine, Inglis County, New South Wales, Australia, cerchiaraite occurs as tiny blocky crystals and sheafs of irresolvable fibres; it forms veinlets from less than 10 to ∼90 μm wide in fractures cutting serandite - quartz - namansilite - mangano-mangani-ungarettiite assemblages. It also replaces these minerals in the rock matrix. It is accompanied by and locally replaces noelbensonite, but in much smaller amounts. These two barium-bearing minerals are among the latest Mn³⁺-rich phases that locally replace Mn²⁺-rich assemblages in the quarry (EJM 16.1.185–189).

At the type locality, the Cerchiara Mine, Borghetto di Vara, La Spezia Province, Liguria, Italy, cerchiaraite-(Mn) occurs as individual grains and radial aggregates with quartz, pectolite, orientite and calcite in fractures that are up to a few millimeters in width. Individual grains are prismatic to acicular, up to 0.1 mm wide and 2 mm long, that form aggregates up to 3 mm across. It is deep green in colour, transparent with a vitreous lustre and a pale green streak (AM 86.197-200).
The cerchiaraite-(Mn) is developed in small fractures and veinlets within metacherts of an ophiolitic sequence during prehnite-pumpellyite facies metamorphism (HOM).
Cerchiaraite-(Mn) from the Cerchiara Mine - Image

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