Gormanite


Gormanite is a phosphate mineral with the formula (Fe,Mg)
3
Al
4
(PO
4
)
4
(OH)
6
·2H2O
. It was named after the University of Toronto professor Donald Herbert Gorman (1922-2020).

Gormanite
Gormanite from the Doce valley, Minas Gerais, Brazil (size: 4.2 x 4.2 x 3.0 cm)
General
CategoryPhosphate minerals
Formula
(repeating unit)
(Fe,Mg)
3
Al
4
(PO
4
)
4
(OH)
6
·2H2O
Strunz classification8.DC.45
Crystal systemTriclinic
Crystal classPedial (1)
(same H-M symbol)
Space groupP1
Unit cella = 11.77, b = 5.11
c = 13.57 [Å]; α = 90.45°
β = 99.15°, γ = 90.05°; Z = 2
Identification
ColorBlue green
Crystal habitAggregates of acicular crystals; pseudomonoclinic
TwinningPolysynthetic around [010]
Cleavage{001} indistinct
FractureSplintery
TenacityBrittle
Mohs scale hardness4-5
LusterSub-vitreous, greasy
StreakPale green
DiaphaneitySemitransparent
Specific gravity3.10–3.13
Optical propertiesBiaxial (-)
Refractive indexnα = 1.619 nβ = 1.653 nγ = 1.660
Birefringence.041
PleochroismStrong, X colorless, Y blue, Z colorless
2V angleMeasured: 53°
References[1][2][3]

Occurrence

It was first described in 1981 for occurrences in Rapid Creek and Big Fish River in the Dawson Mining District, Yukon Territory, Canada. At the type localities it occurs as veins in iron phosphate nodules.[1][3] In the Bisbee, Arizona occurrence, it occurs as large crystals within fractures in a tonalite intrusive. It has also been reported from near Newport, Sullivan County, New Hampshire, and the Charles Davis pegmatite, Groton, Grafton County, New Hampshire. It also has been reported from the Tsaobismund pegmatite, south of Karibib, Namibia.[3]

References

  1. Gormanite, MinDat.org, retrieved 2011-01-30
  2. Gormanite, WebMineral.com, retrieved 2011-01-30
  3. Handbook of Mineralogy


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