142 The American Naturalist. 
group the author describes the crystals in terms of the hexagonal sys- 
tem with a: c — 1: .7233. They are thick, tabular forms, bounded by 
oP, ota oP, $ P2, $ P2 and 4 P 5, and other pyramids with com- 
plicated symbols. . Brégger finds that sections parallel to „P2 extin- 
guish at about 4° from c. 2V = 83° 29’, with a very slight dispersion. 
The angles a, 2 and y are all nearly go°, so that the combination is 
somewhat similar to the combination of orthorhombic aragonites to 
produce an apparently hexagonal form. The axial ratio on the 
assumption of triclinic symmetry becomes a: 6: ¢=.5744: Ti . 5425, 
end the forms OP Poo s co Fy co P PLP, Po als plz, 2 Pa 
* 
Mineral Syntheses.—Boracite has been produced by Gramont’ 
in the wet way. One part of borax and two of magnesium chloride 
were moistened with water and heated to 275°—280° in a sealed tube. 
Little crystals of the mineral thus obtained are bounded by tetrahe- 
drons, octahedrons, and other forms apparently belonging to the regular 
_ system. Each tetrahedral face, however, is observed, upon examina- 
tion, to be composed of small sectors, indicating a grouping of indi- 
viduals of lower symmetry to produce a pseudo-regular form. When 
the mixture was heated at a temperature below 265° (the temperature 
at which natural boracite becomes isotropic) no boracite was obtained, 
but in its stead there resulted elongated hexagonal crystals of somè = 
substance not yet investigated. One part of alumina and two of ue 
Silica, according to Vernadsky,” unite ata white heat to form a glass 
which, under the microscope, is seen to be filled with little needles of SS 
sillimanite, with the composition : SiO, = 37.3! ; Al,O, = 63-65- Pote: o. 
celaine consists essentially of the same substances, viz., a glass holding >? = 
acicular crystals of sillimanite. Many of the most important zeolites = 
have been manufactured by Doelter," who at the same time has solved i 
some of the problems as to their composition, His method of pr% . 
cedure was to dissolve suitable substances at moderately high fi 
tures under pressure, and allow them to cool gradually and crystallize. 
In this way he succeeded in making apophyllite, chabazit cue 
natrolite, and skolecite. The author next proceeded to investigate i 
composition of the minerals formed by heating some specimens to ae 
temperature beyond which they lose water, occasionally a 
them chemically and optically, and by fusing others and studying Ae 
decomposition products, At 260° apophyllite loses 19 P&T cenh 
9 Bull. Soc. Franç. d. Min., XIIL, 1890, p. 252. 
w Tb., p. 256. ; 
u Neues Jahrb. f. Min., etc., 1., 1890, p. 118. 
