| Hellyerite | |
|---|---|
 Zaratite (emerald-green coating), hellyerite (powder-blue) and heazlewoodite (light bronze) | |
| General | |
| Category | Carbonate mineral |
| Formula (repeating unit) | NiCO3·5.5(H2O) |
| IMA symbol | Hy[1] |
| Strunz classification | 5.CA.20 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/c |
| Unit cell | a = 10.77, b = 7.29 c = 18.68 [Å]; β = 94°: Z = 8 |
| Identification | |
| Color | Pale blue |
| Crystal habit | As crystal fragments and microcrystalline coatings |
| Twinning | Fine lamellar parallel to cleavage |
| Cleavage | One perfect, two good at 112° to each other and perpendicular to the perfect cleavage |
| Mohs scale hardness | 2.5 |
| Luster | Vitreous |
| Diaphaneity | Semitransparent |
| Specific gravity | 1.97 |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.455 nβ = 1.503 nγ = 1.549 |
| Birefringence | δ = 0.094 |
| Pleochroism | X = Y = very pale greenish blue; Z = pale greenish blue |
| 2V angle | Measured: 85° |
| Alters to | Decomposes on air exposure |
| References | [2][3][4] |
Hellyerite, NiCO3·6(H2O), is an hydrated nickel carbonate mineral. It is light blue to bright green in colour, has a hardness of 2.5, a vitreous luster, a white streak and crystallises in the monoclinic system. The crystal habit is as platy and mammillary encrustations on its matrix. It is a pentahydrate according to X-ray crystallography. The solid consists of [Ni2(CO3)2(H2O)8] subunits with an extra pair of water of hydration.[5]
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Hellyerite at Webmineral.com
- ^ Handbook of Mineralogy
- ^ Mindat.org
- ^ Bette, Sebastian; Rincke, Christine; Dinnebier, Robert E.; Voigt, Wolfgang (2016). "Crystal Structure and Hydrate Water Content of Synthetic Hellyerite, NiCO3·5.5H2O". Zeitschrift für Anorganische und Allgemeine Chemie. 642 (9–10): 652–659. doi:10.1002/zaac.201600044.