320 The A)ncrican. Geologist. NovembLT, i8itt» 
lows: (i) Corundum will not separate out from a calcium-sodium- 
pctassium silicate magma unless the ratio of alumina to the other 
bases is more than i:i and that of silica is less than 6. (2) It will 
■ net separate unless more than enough alumina is present to unite with 
all the magnesia and iron in the magma. (3) All alumina in a 
magnesium silicate magma, if there is no excess of magnesia, will 
separate as corundum. (4) If magnesia is in excess, the excess will 
unilc with alumina to form spinel, the remainder separating as corun- 
dum. (5) In the presence of chromic oxide in a magnesium silicate 
magma, slight amounts of alumina and magnesia unite with the chro- 
mic oxide to form chromite, but corundum and spinel do not separate. 
(6) In pcridotyte magmas containing alkalies or alkali earths a por- 
tion of the alumina unites with them to form feldspar. (7) The 
tendency of alumina to unite with alkalies or alkali earths to form 
double silicates is strong, but it has little tendency to unite with mag- 
nesia when the magma is a magnesium silicate. m. l. f. 
Experiments relative to the Constitution of Pectolite, Pyrophyllite. 
Calamine and Analcitc. By F. W. Clarke and George Steigek. 
(Am. J. Sci., 158, 245-257.) 
The purpose of the examination was to gain evidence of the chem- 
ical structure of silicates by means of fractional analyses. I. Pectolite. 
The radiated variety from Bergen Hill, N. J., was analysed, the analysis 
giving the accepted formula HNaCaiSiaOu. To determine if this 
represents a true metasilicate, the mineral was ignited, and afterwards 
boiled in a solution of sodium carbonate, with the result that a mean 
of 8.68 per cent, of silica (the amount proportional to the acid hydro- 
gen) went into solution. Boiling the unignited material mineral in 
the sodium carbonate solution, or even with water alone, resulted 
in a slow decomposition with loss of both silica and bases. The loss 
on boiling for 16 hours in distilled water was 4.09 per cent. 2. Pyro- 
phyllite. On strongly igniting, and treating with a solution of sodium 
carbonate, it was found that only 2.84 per cent, of silica was liberated, 
indicating that the mineral may with propriety be regarded as a basic 
salt of the acid H2Si205 with the formula Si.05=Al-0H. Pyro- 
phyllite was only slightly attacked by heating with dry ammonium 
chloride. 3. Calamine. On igniting no definite fraction of water was 
split of¥. Boiling with sodium carbonate dissolved slight amounts of 
silica and zinc, but no breaking up into definite distinguishable frac- 
tions occurred. The evidence, though negative, is in favor of the usual 
formula SiOr.=(ZnOH)2. 4. Analcite. On ignition and treatment 
with sodium carbonate solution only a slight amount of silica was 
split off, indicating the absence of metasilicic acid or an acid meta- 
silicate. On heating with dry ammonium chloride there was again 
very little silica split off, but half of the sodium was converted to 
NaCl, and part of the water replaced by NH3, giving a residue of 
H2Na2Al4Sis024NH3. This points to the original formula of Na4 
Al4SigOa44H20 wliich is contrasted with • the usual formula 
