344 
DESCRIPTIVE MINERALOGY. 
MESOTYPE. 
Zeolite. Clcavcland. — Prismatic Zeolite, or Mesotype. Jameson. — Prismatisclier Kuphon-Spath. Molis. — 
Mesotype. Hauy , Bcudant, Shepard and Dana. — Mesolite. Thomson. 
Description. Colour white, red, yellow and yellowish brown. It 
occurs crystallized, also pulverulent and fibrous. Primary form a right 
rhombic prism. Fig. 326. Mon M'91° 1(7 (Brooke), 91° 4(7 ( Beu- 
dant). Cleavage parallel with M, perfect. Fracture uneven, in some 
varieties coarse earthy. Lustre vitreous. Varies from nearly transpa¬ 
rent to opaque. Brittle. Hardness from 5.0 to 5.5. Specific gravity 
from 2.14 to 2.23. Before the blowpipe, it froths, gives a phosphorescent light, and melts 
into a white semi-transparent enamel; with borax it fuses with difficulty into a transparent 
colourless glass. It is soluble in, and forms a thick jelly with, acids. It becomes electric by 
heat. 
Its power of forming a jelly with acids, and of becoming electric by heat, will distinguish 
mesotype from several minerals which it resembles. Prehnite is harder, and does not form a 
jelly with acids. 
Varieties. The name Natrolite is applied to the yellow and brown varieties, in which the 
fibrous and granular concretions are intersected by laminse. The fibrous variety consists of 
minute crystals aggregated in a radiating or stellular form. When it is very soft, and has an 
earthy fracture, it is sometimes called Pearly zeolite. 
Composition. There is some diversity in the analyses of this mineral. According to Smith- 
son, a specimen from the Faroe islands contained silica 49.00, alumina 27.00, soda 17.00, 
water 9.60. 
Geological Situation. It occurs in cavities and veins in greenstone and trap, and also in 
the gneiss bordering on these rocks. 
New-York County. Minute but 
well defined crystals of mesotype are 
found in veins in gneiss at Harlem, 
where it is associated with apophyllite 
and stilbite. Figs. 327, 328 and 329 
represent the forms which have thus 
been observed. M on o 116° 32'; 
o on o 144° 16k 
This mineral is said also, by Dr. Gale, to occur in the greenstone bowlders on the island. 
Fig. 327. 
Fig. 328. 
LOCALITIES. 
Fig. 329. 
