AMERICAN MUSEUM GUIDE LEAFLETS 
The suite of tourmaline which nearly fills one side of Case 13 is 
notable for the richness of its display of this very striking mineral. 
Both in the foreign occurrences and in those from the United States 
this portion of the collection abounds in beautiful and unusual mounts. 
Especially interesting are the specimens showing unequal distribution 
of color from Haddam, Conn., from Pala, Calif., and from Elba, Italy. 
The Zeolite Division of the Hydrous Silicates (Cases 13 and 14) 
includes some large and finely developed tetragonal crystals of apophyl- 
lite in single individuals and in large and imposing groups. Here are 
also to be found the oddly shaped aggregates of heulandite and stilbite, 
some of which resemble sheaves of wheat, the scattered groupings of 
chabazite and analcite crystals which often give the appearance of 
being strewn over a background of dark rock matrix, and the slender, 
bunched needles of natrolite, springing from a central nucleus like the 
rays of a sun. The zeolites are essentially minerals of the basaltic or 
trap rocks and are mostly to be found in cavities, having been deposited 
in these cup-like hollows by the evaporation of water solutions. 
The Mica Division of the Hydrous Silicates, shown in Case I, 
include minerals which have the distinguishing property of splitting up 
into thin elastic plates or sheets, as in the familiar example of white 
mica or isinglass. | Many species and subspecies are to be found in the 
series displayed, the differentiating characters of which are well shown. 
The remaining species of the hydrous silicates are contained in 
Case 15; a few of the first of these, including clinochlore, strongly re- 
semble the micas in general appearanice but split into sheets which are 
not elastic. 
Serpentine is a hydrous silicate of this division which has not as 
yet been found crystallized, although it often takes the crystal forms of 
other minerals which it has replaced chemically. Many of these re- 
placements or pseudomorphs are to be found in the exhibited series. A 
fibrous form of serpentine, called chrysotile, is interesting as furnishing 
much of the asbestos which is woven into fireproof fabric. Tale and 
sepiolite are also commercially important minerals, the latter furnishing 
us with the meerschaum from which smoking utensils are made. 
Two of the hydrous silicates, garnierite, the silicate of nickel, and chryso- 
colla, the silicate of copper, are ores of their respective metals. 
The last portion of the large class of the silicates includes a number 
of mineral species containing both silicon and titanium or in some in- 
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