Niedermayrite is a rare hydrated copper cadmium sulfate hydroxide mineral with formula: Cu₄Cd(SO₄)₂(OH)₆·4H₂O. It crystallizes in the monoclinic system and occurs as encrustations and well formed vitreous blue-green prismatic crystals. It has a specific gravity of 3.36.

Niedermayrite
General
Category	Sulfate mineral
Formula (repeating unit)	Cu4Cd(SO4)2(OH)6·4H2O
IMA symbol	Ndm[1]
Strunz classification	7.DD.30
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/m
Unit cell	a = 5.543(1), b = 21.995(4) c = 6.079(1) [Å]; β = 92.04(3)°; Z = 2
Identification
Color	Bluish green
Crystal habit	Platy euhedral crystals and as green crusts
Cleavage	Perfect on {010}
Tenacity	Brittle
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	3.292
Optical properties	Biaxial (-)
Refractive index	nα = 1.599 - 1.619 nβ = 1.642 nγ = 1.661
Birefringence	δ = 0.062
2V angle	Measured: 84°
References	[2][3]

Niedermayrite was named for Gerhard Niedermayr (born 1941), an Austrian mineralogist. It was first described in 1998 from a mine in the Lavrion District, Attica, Greece. It is also reported from the Ophir District, Tooele County, Utah.^[2] The environment is in brecciated marble. The cadmium dominant analogue of campigliaite.