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Allargentum & Native Silver

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RMM29329

Allargentum & Native Silver

Collected by seller 2003
Type Locality

Description Tabs

Description
Locality: 
Lawson Mine, Coleman Township, Cobalt, Timiskaming District, Ontario, Canada
Size Range: 
Small cabinet (7-10 cm)
Size: 
9.5 × 6.5 × 5 cm
Description

Weighing approximately 605 grams, this cut specimen was etched out of dolomite to reveal an unusual complete undamaged formation of allargentum which appears as a ribbed "vein" 4cm long and 0.6cm at its widest point.

This formation consists of a graphic intergrowth of allargentum and antimony rich silver ("Silver 2") as can be seen in the photo of an etched polished surface of a similar sample. In that photo the Allargentum is the dark lamellae and the matrix is the antimony rich silver (7-8%Sb). It is interpreted that this "represents exsolutions from an original allargentum that contained more silver than the present allargentum.

Somanchi & Clark (1996) found that a complex intergrowth of Silver2 and allargentum, such as this…forms a homogeneous phase by annealing. They, therefore, suggested that the Silver2-Allargentum intergrowths were formed by deposition of a homogeneous solid solution which subsequently exsolved into antimonial silver (Silver2) and allargentim on cooling." ( Petruk, Harris, Cabri and Stewart; Can Min.V11, Part 1, 1971 p187-195). This allargentum is associated with ordinary leaf silver all of which are on botryoidal Ni-Co arsenides ( nickeline, rammelsbergite, cobaltite, skutterudite etc.) The botryoids are covered in micro size (< 1mm) safflorite and skutterudite crystals.

All the allargentum from Cobalt (the type locality) occurs as graphic intergrowths but as far as I know this is the first time such formations have been found. This is the best and largest of half a dozen such formations that I found in 2003 and it is extremely unlikely that anymore will be found.

Mineral Data
What's on the rock

Allargentum

Formula: 
(Ag1-xSbx)
Strunz: 
2.AA.30
Crystal System: 
Hexagonal
Hardness: 
3.5
Colour: 
Silver
Type Locality: 
University Mine (Giroux Lake Mine), Coleman Township, Cobalt area, Cobalt-Gowganda region, Timiskaming District, Ontario, Canada

Silver

Formula: 
Ag
Strunz: 
1.AA.05
Crystal System: 
Isometric
Hardness: 
2.5 - 3.0

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