Pimelite

Pimelite
Pimelite from Szklary, Lower Silesia, Poland. Specimen size 2.3 cm (0.9 in)
General
Category	Phyllosilicates
Formula (repeating unit)	Ni3Si4O10(OH)2·4H2O[1]
Strunz classification	8/H.09-65 (8 ed)
Dana classification	71.3.1b.5
Crystal system	Hexagonal Unknown space group
Identification
Formula mass	554.5 g/mol[2]
Color	Bright green, apple green, yellow-green
Crystal habit	Fine-grained, also fibrous
Cleavage	None
Fracture	Uneven to conchoidal
Mohs scale hardness	2.0–2.5
Luster	Waxy
Streak	White
Diaphaneity	Translucent
Specific gravity	2.23–2.98
Optical properties	Biaxial (−) Can appear isotropic due to fine grain size[3]
Refractive index	Nx = 1.592 Ny = 1.615
Pleochroism	Pale green, colourless to light yellow green
Solubility	Decomposed by acids[3]
Other characteristics	Neither radioactive[1] nor fluorescent[4] Expands to 17.35 A using glycol[4] Nonmagnetic[2]
References	[1][2][3][4]

Pimelite was discredited as a mineral species by the International Mineralogical Association (IMA) in 2006, in an article which suggests that "pimelite" specimens are probably willemseite (which is approved), or kerolite (which is also discredited). This was a mass discreditation, and not based on any re-examination of the type material (assuming any exists).^[5] Nevertheless, a considerable number of papers have been written, verifying that pimelite is a nickel-dominant smectite.^{[4][6][7][8][9]} It is always possible to redefine a mineral wrongly discredited.^[5]

The mineral was erroneously assumed to be a nickel-rich talc in a paper published in the American Mineralogist in 1979,^[10] but it had already been determined to be a smectite as early as 1938, and this was confirmed in another article in the American Mineralogist in 1966.^[8] Both nickel-bearing talc and nickel dominant smectite occur at the type locality, Szklary, Ząbkowice Śląskie County, Lower Silesia, Poland.^[4]