reflection
of the satin spar, by means of the scales of a small river-fish called
the bleak, that are suspended in dissolved isinglass, and dropped into
the bulbs, which are then turned in all directions in order to spread
the solution equally over their interior surface; in this way the glass
bulbs assume the natural color and brilliancy of satin spar; they are
harder, however, and it is easy to detect them on that account.
Fine specimens may be seen at the New York Lyceum of Natural History, also in the collection of Dr. Gay, of Boston.
Satin
gypsum, which bears the greatest resemblance to satin spar, and only
differs in its chemical constituents (having sulphuric acid, instead
of carbonic, as a component part), is much used for the same kind of
ornamental purposes, and is more abundant over the world. I have seen
very splendid specimens at South Boston, in the beautiful collection
of minerals belonging to Francis Alger, Esq., who brought them from
Nova Scotia, and who (as also Dr. C. T. Jackson) has given so valuable
a description of all the mineral treasures of that province.
Satin
gypsum is, however, much softer than satin spar, and is much easier
scratched; for which reason it is not so generally employed.
ALABASTER.
This
mineral is a compact gypsum, and occurs massive, with a compact
fracture; it is translucent; has a glimmering lustre, and its colors
are white, reddish, or yellowish.
The
purest kinds of this mineral are used in Italy for vases, cups,
candlesticks, and other ornaments. It is found at Castelino, in
Tuscany, thirty-five miles from Leghorn, at two hundred feet below the
surface of the earth.
