New Occurrence Of Yugawaralite From The Chena Hot Springs Area, Alaska¹ Available to Purchase

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 ų;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, H₂O^–2.79, 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.