Knoxville journal. [volume] (Knoxville, Iowa) 1874-1986, 1874-06-11
A Precious Sandstone.

To THE sandstone or quartz family be
long some very fine gems. Sand, besides
appearing in 80 many lower forms, con
stitutes the base Of series OF precious
stones, the most beautiful of which is the
noble opal. That greatly. esteemed gem
when chemically considered, becomes
simply sandstone, for it consists almos
entirely of uncrystallized or amorphous
silica, combined with little water.
When held between the eye and the
light the opal has peculiar, milky color
verging on semi-transparency; when
viewed by reflected light it gives off the
hues of the rainbow. This prismatic
quality has proved an inexplicable one to
the mineralogists. By some it is thought
to arise from very minute assures in the
surface of the stone; the Able Hauy at
tributes it to films of air in cavities in the
interior; Brewster to inferior assures
alone. And DR.. Feuchtwanger says: Ii
is my opinion, sufficiently plausible, that
the unequal division of smaller and larger
cavities, which are filed with water, pro-
duces the prismatic colors, and for the
simple reason that the opal, which grows,
after while, dull and Opaque, may be re-
stored to its former beauty if put for a
short time into water or OIL"
The opal is found chiefly in Hungary
and South America. In the former coun-
try the mines near the village Of Ger
winceza date from the year 140O, and
were probably worked before that time.
Though sometimes bearing the name
Oriental" these gems have never been
native in the East within our knowledge.
The ancient traders probably found the
rage for foreign merchandise quite as
great in their day as it is in ours, and as
a consequence many Hungarian opals
made journey to the Indies and re-
turned thence as an Oriental production.
This gem was known to the ancients,
as we learn from Pliny, who describes ii
as combining the colors of the ruby, the
amethyst, the topaz and the emerald. To
the superstitious believers in the occult
powers of gems this combination of the
attributes of so many valuable stones
gave great significance to the opal.
The maximum size of the opal is sell
dom greater than that of hickory nut,
and specimens so large are very rare.
Fine opals were probably even scarcer
with the ancients than with US. Pliny,
in describing this gem, says that it had
sometimes attained the size of hazel
nut, and speaks as though the specimens
then known were rarely or never so large.
The most celebrated opal is in the I'M
perial Cabinet in Vienna. 1t measures
four and three. quarter inches in length
and two and half in thickness, and
weighs seventeen ounces. 1t displays
magnificent colors and is in every respect
a perfect stone.
Opals are usually cut en- ca5ochon Tor
oval) on both sides. They are brought to
this form by grinding on leaden wheel,
kept busted with -four of emery, and are
then polished, with rotten-stone and
water, on wooden wheel. Lastly, they
are rubbed with some slightly oily sub
stance, such as putty, applied on piece
OF wash.leather, and are then ready for
mounting or setting.
The present money value of the opal
can scarcely be arrived at by any fixed
rule, as it largely depends on the play of
colors, and that varies more or less with
every stone. Ordinary specimens may be
had at from 81 to $40 per carat, but for
large or exceptionally fine ones the price
is generally regulated by the anxiety of
the purchaser. An opal exhibited at the
London Worlds Fair in 1851, weighing
5261% carats, or near four and q hall
ounces Troy, was valued a. $4,000. For
the specimen in the Vienna Cabinet, men
toned above, $25O,0O0 have been offered
and ed.-AppIeton's Journal.