Scientia Sinica

180 SCIENTIA SINICA Vol, V

420° and 410°C respectively, yielded a product that differs from natural cancrinite somewhat in intensities but not in spacings. The higher temperature product (Expt. 7, 475°C), however, showed a slightly but distinctly expanded lattice.

When NaCl solution was tried, much margarite and some boehmite appeared in the final product (Expt. 8).

In later experiments (Expts. 9, 10, 11) an excess of Ca salts was added. Five times as much Ca equivalent as would be required by the formula of margarite was introduced into the charge. With CaCl,, the final product consisted solely of margarite. When CaCO; was used, much of it recrystallized as calcite and only part of it went into margarite formation. If CaO was added, margarite would not form at all; an unknown compound “A”, which resembles sodalite in x-ray pattern, was the only product.

Unknown “A” appeared in-both Expts. 7 and 11. As shown in Table 1, the chemical composition of the initial charge should make the product more like hauynite than sodalite, if the final product would be feldspathoid at all. However, x-ray analysis showed the reverse to be true. Barth"! gives. the a-dimension of the unit cell of sodalite as 8.89 A, and that of hauynite, 9.11 A. The synthetic product gives 8.84 A, showing a slight shrinkage as compared with sodalite, and may have the composition of a Ca-sodalite. As far as we know, no pure Ca-sodalite has ever been reported in nature. However, Barth states that “the essential constitution in the hauynite system are noselite silicates: NasAl,Si,O2,° SO, and Silicate II: Ca,A1,Si,O, ° SO,”. It is probable that unknown “A” chemically resembles Barth’s Silicate III.

So far the experimental results show that in the presence of CaCl, margarite formed more readily than otherwise. Therefore, in further experiments (Expts. 15, 16, 17, and 18) with different temperatures, CaCl, was added in large excess. The results indicate that below 350°C the products consisted solely of boehmite. At 370°C in 16 days, boehmite plus a little margarite formed. It appears likely that the lower temperature boundary of margarite formation in slightly acid solutions lies in the range 350-370°C. The upper temperature limit of margarite formation was not determined. It

must be much higher than 500°C (Expt. 19).

Expt. 12 (415°C) was tried to see if a Na-margarite, in which Ca is replaced by Na, could be synthesized. The initial charge consisted of Al(OH), “Acid Silicie”, and NaCl. Only boehmite and paragonite showed in the product. Runs at other temperatures gave essentially the same result.

Expt. 13 was an attempt to prepare clintonite (H,Ca Mg; Al,Si,O,2). It is a brittle mica with Mg replacing part of the Al in the margarite structure. The initial charge had an Al:Si:Mg ratio of 2:2:3 as called for by the formula, but with an excess of Ca. The product gave an x-ray pattern of serpentine.