Scientia Sinica

No, | TU: PRELIMINARY RESULTS ON HYDROTHERMAL SYNTHESIS OF BRITTLE MICAS 179

be controlled as far as the oxidation state of iron went. As a result, iron had to be discarded.

The identification of the products was made primarily by x-ray diffraction method. Powder photographs were taken in precision cameras of 57.3 mm radius. Due to the very fine crystalline nature of the product, optical identification was impossible except for a rough determination of the refractive indices.

The results of the more representative runs are listed in ‘Table 1.

_ Discussion oF EXPERIMENTS

Margarite, the Ca brittle mica, has the theoretical formula: CaAl, (Al,Si,01) (OH). The simplest equation of its formation from oxides may be expressed as follows:

CaO ap 2A1,0; ae 2810, Se H,0 Te CaAl, (AL,Si,0 9) (@H),

Therefore, as shown in Table 1, the Al,O;: SiO, ratio was kept at 1:1. The starting substance consisted of Al(OH);, “Acid Silicic,” and various amounts of Ca salts. When attempts were made to synthesize members of Fe-free brittle micas other than margarite, the Al,O3: SiO, ratio was changed to that called for by the desired product.

It was realized at the beginning that because of the large proportion of Al(OH); present in the initial charge, much of it probably would crystallize out as boehmite unless solutions used were rather basic or acidic, or, unless excessive Ca salt was added, which might retard this tendency. This was exactly shown to be the case; earlier experiments (Expts. 1, 2 and 3) gave much boehmite and some margarite when the ingredients were in the molecular proportion of margarite.

Therefore, in Expts. 4-7, NaOH or Na,CO; was added to the initial charge in the hope that it might serve as an agent to give a relatively strong alkalinity. The results, however, were discouraging, as invariably cancrinite NasCa, (AI,SisO2,) (CO;, SO,) -3H,O formed. According to Betechtin™!, cancrinite may contain as little as 0.3% of CO,.. NaOH used in our experiments contains 1.57, of Na,CO3. Apparently, even the presence of a very small quantity of CO; tends to shift the reaction in favour of cancrinite”,

A comparison of x-ray patterns of these synthetic cancrinites with the natural mineral reveals an interesting phenomenon. Lower temperature cancrinite (Expt. 6, 370°C) corresponds very well in both spacings and intensities with cancrinite from Renfrew Co., Ont., Canada. Expts. 4 and 5, at

1) Cancrinite has been identified a number of: times in hydrothermal mineral synthesiel6, 7, 14] and also recently in boiler deposits[5],