Abstract

Yugawaralite (CaAl2Si6O16·4H2O), a relatively rare calcium zeolite, was found in a new locality near Chena Hot Springs, east-central Alaska in a geologic setting that diffesrs from that described for occurrences in Japan and Iceland. It occurs as well-formed, quartz-encrusted crystals up to 8 mm long, elongate along the a axis and tabular parallel to {010}. Principal forms are {001}, {010}, {100}, {021}, and {111}.

The zeolite is monoclinic, space group Pa; a = 10.043 ±0.002, b = 13.997 ± 0.003, c = 6.725 ±0.002 Å; β = 111°11'±1'; a:b:c=0.7175:1:0.4815; volume = 881.5±0.2 Å3;Z = 2. Strongest X-ray diffraction lines (in Å) are: 3.056 (100), 4.668 (73), 5.81 (64), 4.642 (64), 6.99 (60), and 4.293 (32). Optically it is biaxial (—); α = 1.492±0.002, β = 1.498±0.002, γ = 1.502 ± 0.002; 2V = 71°±2°;r<v distinct; Z = b, X Λc = –9°. The hardness is 5+; cleavage {100} and (401) distinct, {101} imperfect; density = 2.22±0.01 (measured), 2.225 g.cm−3 (calculated). These data agree with refined data obtained for yugawaralite from the type locality; however, none of the topotype material examined was optically positive, as reported by previous workers.

Chemical analysis shows SiO2 61.47, Al2O3 17.38, Fe2O3<0.04, TiO2<0.01, MgO<0.01, CaO 8.51, SrO 0.21, Na20 0.06, K20 0.09, H2O+ 9.33, H2O2.79, total 99.90 wt. %. An apparent deficiency of cations [Al2O3/(R2O+RO) = 1.09] disappears if H+, which is 0.3737 ions per formula in excess of that required by an ideal 8H2O in the unit cell, is present as oxonium ion.

Thermogravimetric analysis gives good agreement with TGA curves from the type locality. Ion-exchange values determined show a low-exchange capacity as compared with most zeolites. Infrared absorption spectra obtained are distinctive but have similarities to those of the heulandite group.

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