a Mineral, which occurs crystallised and
massive. Primary form a right rhombic prism. Cleavage easy, parallel to
the base of the primary form, and less so in the direction of the
lateral faces. Fracture uneven. Hardness, scratches glass easily.
Becomes electric by heat. Colour white, gray, and various shades of
green and greenish-yellow. Lustre vitreous. Transparent, translucent.
Specific gravity. 2-926. The variety which occurs in small thin
crystals is called Koupholite. The crystals of this substance have a
remarkable tendency to exhibit rounded faces.
Massive varieties botryoidal, globular,
and stalactitic, structure
broad fibrous; amorphous, structure granular, compact, with rougli
surfaces. It occurs also in rolled masses.
Before the blow-pipe it is converted
into a white scoria, and fuses into a compact globule; with borax it
readily becomes a clear glass.
This mineral was first found at the Cape
of Good Hope; it has since
been met with in many places in different quarters of the. globe, as
Scotland, Cornwall, France, &c. Koupholite occurs at Baregra in
the department of Hautes-Pyre'nees. It is composed of silica, alumina,
lime, oxide of iron, potash, soda, and water. The following forms of
Prehnitc are given by Dana :— fSlcllite. In fibrous stellar groups like
mesole; lustre silky and shining. It fuses to a white enamel
Gelatinizes with muriatic acid. It comes from Kilsyth, Scotland.