Katayamalite

(repeating unit)KLi₃Ca₇Ti₂(SiO₃)₁₂(OH)₂IMA symbolKyl^[1]Strunz classification9.CJ.25Dana classification61.01.04.02Crystal systemMonoclinicCrystal classPrismatic
H-M symbol: 2/mSpace groupB2/bUnit cell3,179.12IdentificationColorWhiteCrystal habitTabular, common twinningCleavagePerfect on {001}Mohs scale hardness3.5 - 4LusterVitreous, pearlyStreakWhiteDensity2.91Optical propertiesBiaxial (+)Refractive indexn_α = 1.670
n_β = 1.671
n_γ = 1.6772V angleMeasured: 32
Calculated: 46DispersionStrong
r > vUltraviolet fluorescencebrilliant blue-white under SWOther characteristics Radioactive

Katayamalite is a cyclosilicate mineral that was named in honor of mineralogist and professor Nobuo Katayama. It was approved in 1982 by the International Mineralogical Association, and was first published a year later.^[2]

Relation with baratovite

Katayamalite is the hydroxyl analogue of baratovite and the hydroxyl end member of the series,^[3] but was first described as a fluor-dominant mineral. Some scientists claim it to be rather hydroxyl- than fluor dominant, which would make baratovite isostructural with it. It would make the two minerals the same species, with baratovite having priority. As the case hadn't been clarified, katayamalite remains an IMA-approved mineral until this day.^[2]

Chemical properties

Katayamalite mainly consists of oxygen (43.16%), silicon (24.25%), calcium (20.18%), but otherwise contains titanium (6.89%), potassium (2.81%), lithium (1.50%). It has trace amounts of fluorine (0.68%), sodium (0.41%) and hydrogen (0.11%) in its composition as well. It has a barely detectable radioactivity, 40.21 measured in Gamma Ray American Petroleum Institute Units. The concentration of it in percentage is 2.49. It was originally described as having a triclinic symmetry in 1985, but the structure was redetermined to be monoclinic in 2013. It has a radiant blue-white fluorescence, and platy morphology.^[2]

Occurrence

The mineral is associated with sugilite, albite and aegirine.^[2] Crystals are usually twinned. This mineral can be found in aegirine syenite.^[3]

References