MINERALOGY. 70 
Beryis of great beauty are found in the granite of Mertschinsk, as also in 
the Ural and Altai mountains, and near Rio Janeiro. Beryls of enormous 
size occur in the United States. One specimen from New Hampshire 
weighs 240lbs., and is four feet in length. The lateral faces of well-formed 
crystals of beryl are generally striated vertically. In its composition 
it consists of a combination of silicate of glucina with silicate of alumina. 
18. Prehnite (silicate of alumina and lime). 
This mineral occurs in volcanic and primary rocks in the Tyrol, 
Piedmont, Carinthia, Salzburg, Sweden, Norway, and the United States. 
Its crystals belong to the trimetric system, and are derivatives of the forms 
in fig. 62, pl. 34. Prehnite generally occurs in rhombic prisms ; it is also 
found granular, foliated columnar, and amorphous. It is a combination of 
silicate of alumina with silicate of lime, and water. 
19. Nepheline. 
Nepheline, a variety of which is called elaeolite, occurs both amorphous 
and crystallized: its crystals belong to the hexagonal system. It is 
transparent or translucent, of conchoidal to splintery fracture, generally of 
an oil-green color, but is sometimes blue, red, and brown. It consists of 
silicate of alumina, silicate of potash, and silicate of soda. 
20. Scapolite and Wernerite. 
The first named mineral bodies, besides lime and alumina, contain a small 
quantity of potassa and soda, wanting in Wernerite. Both are colored by a 
slight admixture of oxydes, especially of iron. Both crystallize in the 
dimetric system. Scapolite occurs in forms like fig. 46; Wernerite like 
fig. 53, pl. 34. Scapolite occurs in the volcanic rocks of Vesuvius, and is 
abundant in some crystalline rocks, especially granular limestone, 
occurring in many places in the United States; Wernerite in Sweden, 
Norway, Finland, and various parts of the United States. 
21. Lolite, or Dichroite. 
This mineral is remarkable for its color, which, in one position, appears 
indigo-blue, and at right angles to this, yellow or brown. It occurs amor- 
phous and crystallized, the crystals belonging to the trimetric system 
( pl. 34, fig. 71). They are found imbedded in granite. It thus occurs in 
Sweden, Norway, Finland, and in the Northern United States. It is some- 
times polished, and used as a gem. 
22. Themsonite. 
This mineral is met with in Scotland, both amorphous and crystallized, 
The crystals belong to the dimetric system ( jig. 50), have a smooth surface, 
vitreous lustre, and white color. They-are more or less translucent to 
transparent. This mineral consists of silicates of lime, soda, and alumina, 
with water. 
23. Natrolite. 
Natrolite occurs both amorphous and crystallized, and sometimes forms a 
very beautiful mineral of a white, whitish-yellow, or reddish color. Its 
crystallizations are often globular forms covered with fine needle-shaped 
crystals (pl. 35, fig.4). They belong to the trimetric system ( pl. 34, fig. 59). 
Natrolite, in addition to soda, alumina, and silica, contains water, and 
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