DEPARTMENT OF GEOLOGY 
67 
is, of lime, baryta, and strontia includes materials of varying 
values and properties. With them are placed also the com- 
pounds of magnesia. 
Fluorite, which is characterized by the frequent occurrence 
of large crystals and brilliant colors, is here illustrated princi- 
pally by the duller and more massive specimens of industrial 
value. This mineral is mined in large quantities for use as a 
flux and in the compounding of glazes, enamels, opaque glass, 
and similar materials. Minor uses and the chemical indus- 
tries also consume considerable quantities. 
Magnesite, the carbonate of magnesium, is represented by a 
small number of specimens, as it occurs in but few places, in 
which, however, it is extensively mined for its use as fire-resist- 
ing material, tiles, artificial marble, and even carbonic acid. 
Native epsom salt, sulphate of magnesia, from several locahties, 
is also shown. Barite, the sulphate of barium, is represented 
by a series of specimens from many localities. The large series 
of crystals of this mineral shown is exceptional, as the massive 
form is usual in deposits of economic value. This material is 
largely ground for paint. The carbonate of barium, witherite, 
and strontianite, the sulphate of strontia, useful for colored fire 
and for sugar refining, are included here. 
Common salt is represented by a large series of specimens 
both of the crude salt and of the forms in which it is prepared 
for the market in different parts of the world. A large series of 
African salt is included here. 
Lithia compounds are represented by a large group of its ore, 
lepidolite, with an associated bright red tourmaline, rubelHte, 
and also by its other common ore, spodumene, from various 
localities. 
Miscellaneous soda -bearing minerals are represented by a 
series of specimens including natural carbonate of soda of sev- 
eral varieties from different localities, and natural sulphate of 
soda. The fluoride of soda and aluminum, cryolite, and its uses, 
is represented by a complete series of specimens showing all 
stages of manufacture from the crude mineral to ordinary and 
caustic soda, alumina and alum. 
An unusually large and complete collection is that of the 
“Stassfurt Salts” which are soluble compounds of potash and 
magnesia from which nearly the whole of the world’s supply of 
potash is drawn. With these are shown the more important 
potash compounds which are made from them. 
