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Arfvedsonite crystal
© Doug Merson
Arfvedsonite crystals
© Doug Merson
Arfvedsonite crystal
© Stephan Wolfsried
Na(Fe+2,Mg)Fe+3Si22(OH)
Arfvedsonite is a common amphibole at Mont Saint-Hilaire. It can be found in pegmatite dikes up to 20cm and as black prisms in marble xenoliths. Fresh crystals are black and display a vitreous to dull luster, while in altered pegmatites the crystals may be partially altered or etched. Magnesio-arfvedsonite and fluoro-magnesio-arfvedsonite are also found at MSH, they are indistinguishable from each other without chemical analysis.
PHYSICAL CHARACTERISTICS:
Color is dark green to gray, black.
Luster is vitreous to dull.
Diaphaneity is opaque.
Crystal System is monoclinic; 2/
Crystal Habits include excellent prismatic crystals, prisms and pitted
somewhat fibrous crystals.
Cleavage: {110} is perfect.
Fracture is uneven to subconchoidal.
Hardness is 5 to 6.
Specific Gravity is approximately 3.1 g/cm
Streak is dark blueish grey.
Associated Minerals include chkalovite, erdite, kogarkoite,
makatite, natrophosphate, rasvumite, revdite, sazhinite-(Ce), sidorenkite, thalcusite, tugtupite, vitusite-(Ce).
Distinguishing Features: Crystal habit.
Origin: Named in 1923 after Johan A. Arfvedson (1792-1841), Swedish chemist.
CLASSIFICATION:
Dana System
# 66.1.3c.9
Strunz Classification
# VIII/F.8-100
REFERENCES:
MinRec 21:296 (1990), CanMin 34:1011 (1996), Dana 8:1364-1365 (1997)
DISTRIBUTION AND RARITY AT MONT SAINT-HILAIRE:
MSH
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