285 
on Basalt , See. 
the spheroids are rendered imperceptible to the eye, they are 
not obliterated, and their rusty surfaces are often disclosed by 
an attempt to fracture the mass. 
5th. A continuation of the temperature favourable to arrange- 
ment, speedily induces another change. The texture of the mass 
becomes more granular, its colour rather more gray, and the 
brilliant points larger and more numerous : nor is it long before 
these brilliant molecules arrange themselves into regular forms ; 
and, finally, the whole mass becomes pervaded by thin crystalline 
laminae, which intersect it in every direction, and form pro- 
jecting crystals in the cavities. The hardness of the basis seems 
to continue nearly the same ; but the aggregate action of the 
basis, and of the imbedded crystals, on the magnetic needle, is 
.prodigiously increased. It appears to possess some polarity; 
<and minute fragments are suspended by a magnet. Its specific 
gravity is somewhat increased, as it is now 2.949. The crystals 
contained in it, when examined by a microscope, appear to be 
fasciculi of slender prisms, nearly rectangular, terminated by 
planes perpendicular to the axis ; they are extremely brilliant ; 
their colour is greenish-black ; they are harder than glass, and 
fusible at the blowpipe; they are suspended by the action of a 
magnet. They are arranged nearly side by side, but not accu- 
mulated in thickness, so that they present the appearance of 
broad thin laminae; they cross one another at all angles, but 
always on nearly the same plane ; and the lamina thus formed 
is often three or four lines long, and from a line to a line and a 
half broad, but extremely thin.* 
* It may be observed, that the cavities which existed in the glass are not obliterated 
during the subsequent processes, though their interior surfaces undergo some change. 
The minute globules first formed often become prominent, and project into the cavities. 
