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Formula: Na8Mn2Si10O25(OH,Cl)2.12H2O
Phyllosilicate (sheet silicate), manganese-bearing mineral
Crystal System: Orthorhombic
Specific gravity: 2.31 measured, 2.32 calculated
Hardness: 4
Streak: White
Colour: Pale brownish yellow to orange
Environments
Although Varennesite was approved in 1994, to date (September 2024) it has been reported only from the type
locality.
Localities
At the type locality, the Demix-Varennes quarry, Saint-Amable sill, Varennes & St-Amable, Lajemmerais RCM,
Montérégie, Québec, Canada, the nepheline syenite sill
intrudes shale and
limestone. On a microscopic scale, the rock is quite porous, with
many small cavities hosting a complex suite of rare minerals. Besides the large number of rare species, the most
significant mineralogical feature of the sill is the abundance of apparent
primary natrolite.
Varennesite is a rare species as only about 10 specimens, each containing only a few milligrams of material,
have been found to date (1995). It appears to be a primary,
late-stage mineral of the sill and is most commonly associated with
eudialyte, aegirine,
natrolite, serandite,
manganoneptunite,
microcline, albite and
zakharovite. Other associated species include
astrophyllite,
villiaumite, makatite and
vuonnemite
(CM 33.5.1073-1081).
Varennesite from the Demix-Varennes Quarry -
Image
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