Motukoreaite , Phillipsite Locality: Stradner Kogel Mt., Wilhelmsdorf, Bad Gleichenberg, Styria, Austria Yellowish-white balls of Motukoreaite together with Phillipsite. Field of view 6 mm. Depth of field is achieved with CombineZM. Specimen and photo Leon Hupperichs. — Photo: Leon Hupperichs · CC BY-SA 3.0
Motukoreaite
A magnesium-aluminium sulfate-hydroxide named for Motukorea island, New Zealand.
Intro adapted from Wikipedia (CC BY-SA).
Motukoreaite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Mg₆Al₃(OH)₁₈[Na(H₂O)₆](SO₄)₂·6H₂O.
It crystallizes in the hexagonal crystal system (space group R-3m). It is a member of the Woodwardite structural group.
Key properties: Mohs hardness 1–1.5; specific gravity 1.43–1.53; Dull luster; refractive index 1.51; optically uniaxial.
IMA symbol Mtu, IMA status: questionable, named in 1976.
Relatively common in assemblages formed by reaction of basalt volcanoclastics with sea-water; in cavities in a haüyne-nephelinite.
It is found associated with Olivine, pyroxene, calcic feldspar, magnetite, calcite, gypsum, barite, hisingerite, zeolites, “limonite”, quartz (Brown’s Island, New Zealand); hydrotalcite.
The name comes from Motukorea, island of cormorants, the Maori name for Brown’s Island, New Zealand.