Gormanite

Gormanite is a phosphate mineral with the formula (Fe,Mg)₃Al₄(PO₄)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 × 4.2 × 3.0 cm)
General
Category	Phosphate minerals
Formula	(Fe,Mg)3Al4(PO4)4(OH)6·2H2O
IMA symbol	Gm[1]
Strunz classification	8.DC.45
Crystal system	Triclinic
Crystal class	Pedial (1) (same H-M symbol)
Space group	P1
Unit cell	a = 11.77, b = 5.11 c = 13.57 [Å]; α = 90.45° β = 99.15°, γ = 90.05°; Z = 2
Identification
Color	Blue green
Crystal habit	Aggregates of acicular crystals; pseudomonoclinic
Twinning	Polysynthetic around [010]
Cleavage	{001} indistinct
Fracture	Splintery
Tenacity	Brittle
Mohs scale hardness	4–5
Luster	Sub-vitreous, greasy
Streak	Pale green
Diaphaneity	Semitransparent
Specific gravity	3.10–3.13
Optical properties	Biaxial (−)
Refractive index	nα = 1.619 nβ = 1.653 nγ = 1.660
Birefringence	.041
Pleochroism	Strong, X colorless, Y blue, Z colorless
2V angle	Measured: 53°
References	[2][3][4]

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.^[2][4] 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.^[4]