1396.] Mineralogy and Crystallography. 935 
ments on heulandite. Anhydrous H,SO, abstracts 2 H,O from the 
molecule Ca Al, Si,O,, -+ 6 H,O leaving Ca Al, Si,O,,+4H,O. The 
latter compound is optically quite different from the original heulan- 
dite, having, for example, a much higher double refraction and a dif- 
ferent plane of the optical axes. The change may be watched under a 
microscope, and takes place faster in some crystallographic directions 
than in others. Dilute sulphuric or hydrochloric acid gives a pseudo- 
morph, which, after heating, is composed of almost pure SiO, (only 1.33 
per cent bases). It has a specific gravity of 2.143, is optically biaxial 
with a small angle, and has weak double refraction. It is regarded as 
a new modification of SiO,, probably like Seacchi’s “ granulin.” 
In continuation of his studies on Algerian minerals, Gentil’ mentions 
with more or less detail calamine, smithsonite, sphalerite, calcite, 
galena, cerussite, limonite and barite from a number of zine mines, 
Ilvaite and bustamite from Cape Boujaroun are also studied somewhat 
at length.—Dufet” publishes the results of a crystallographic study of 
four modifications of indophenol, also of several complicated organic 
and inorganic compounds which are not at all related to one another. 
` —Lacroix” describes the microscopical characters of a number of 
compact or earthy minerals. They are not amorphous, as they appear 
to the naked eye, but are all micaceous and crystalline in ultimate 
structure.—Termier” reports seven new forms, and a large number of 
rare ones, on a quartz crystal discovered on a block of gneiss in the 
lateral moraine of the lower Grindelwald glacier. The new forms are 
7.7.0.4 
32.15.17.62 
11.25.36.0 
10.35.25.20 
1.4.52 
17.4.21.9 
3.4.7.7 
The explanation of these rare faces is sought in the deposition of cal- 
cite on the quartz, followed by the formation of “ temporary limiting” 
faces as the crystal again grows, and, finally, the solution of the out- 
° Bull. Soc. Fr. Min., XVIII, pp. 399-414, 1895. 
1 Bull. Soc. Fr. Min., XVIII, pp. 414-426, 1895. 
4 Bull. Soc. Fr. Min., XVIII, pp. 426-430, 1895. 
22 Bull. Soc. Fr. Min., XVIII, pp. 443-457, 1895. 
