The group of Spinel includes in mineralogy a number of species of
different though analogous composition. The Spinel employed as a gem is
almost wholly confined to the magnesium aluminate, having the percentage
composition alumina 71.8 and magnesia 28.2. This is usually of a red
color, different shades giving gems known by different names as follows:
Deep red, spinel-ruby; rose-red, Balas ruby; yellow- or orange-red,
rubicelle; violet red, almandine ruby. Spinel is thus known among gems
chiefly as a relative of the ruby, and this sort of Spinel will first be
considered.
The Spinel rubies differ from the true or corundum rubies in hardness,
specific gravity and system of crystallization. The hardness of Spinel
is 8, or about that of topaz, and the specific gravity 3.6. It is thus
neither as hard nor as heavy as corundum ruby. Again, the system of
crystallization differs. Spinel crystallizes in the isometric system and
is usually found in the form, of octahedrons, while corundum ruby is
hexagonal in crystallization. (See colored plate in November number.)
Spinel is singly refracting in polarized light and corundum doubly
refracting. Spinel ruby is infusible before the blowpipe, but on heating
undergoes a curious series of changes in color which are quite
characteristic. The red changes first to brown, and then becomes black
and opaque, but on cooling the black changes to green, then becomes
nearly colorless and finally the stone resumes its original red color.
As a small percentage of chromium is usually found by analysis to exist
in ruby Spinel, its color is generally considered to be due to this
ingredient. While the Spinel ruby is considered of less value than the
corundum ruby and is sometimes by fraud or error substituted for the
latter, it yet has a definite value as a gem and is sold under the name
of Spinel ruby or some of its varieties. This value is usually reckoned
at about half that of the corundum ruby, although variations in quality
of the stones, as well as changes in demand, cause differences of price.
Thus Emanuel mentions a Spinel ruby of good quality weighing 40 carats,
which in 1856 was sold for two thousand dollars, but which in 1862
brought at public auction only four hundred dollars. In 1866, however,
it was again sold for twelve hundred dollars. The Spinel ruby of the
French crown jewels, weighing 56 carats, was in 1791 valued at ten
thousand dollars.
Not only is Spinel ruby related to corundum ruby in color and use, but
the two are frequently associated together in nature. The gem gravels of
Ceylon, Siam, Australia and Brazil contain both kinds of rubies, and the
ruby mines of Upper Burmah, where the corundum ruby occurs in a
crystalline limestone, produce also large quantities of Spinel rubies.
Spinel rubies also come in large quantity from Badakschan, in
Afghanistan, near the river Oxus, the name of Balas rubies, by which
they are often known, being said to be derived from Beloochistan, or
Balakschan. The Persians have a tradition regarding these mines that
they were disclosed by an earthquake which rent the mountain in twain.
The localities above mentioned furnish nearly all the Spinel rubies of
commerce. A few have been found in North America at Hamburgh, New
Jersey, and San Luis Obispo, California. But these localities have never
afforded any appreciable supply. No Spinel rubies of great size are
known. Bauer mentions as the largest known, two cut stones, one of 81
carats and the other 72½ carats, exhibited at the London Exposition of
1862. The King of Oude is said at one time to have possessed a Spinel
ruby the size of a pigeon’s egg.
Spinel occurs in many other colors besides red, such as orange, green,
blue and indigo, as well as white and black. Occasionally colorless
Spinels occur, and as they cannot be distinguished by their behavior in
polarized light from the diamond, it is sometimes sought to substitute
them for the latter. They can be detected at once, however, by their
inferior hardness. While Spinels of any color, if transparent and free
from flaws, make desirable gems, the only colors found in sufficient
quantity outside of the red to make an appreciable supply are the blue
and the black. The blue Spinels resemble the sapphire in color, though
they are somewhat paler. They come chiefly from Ceylon and Burmah, where
they occur together with the ruby Spinel. The black Spinel is known as
Ceylonite, or pleonaste, and is also obtained chiefly from Ceylon,
although occurring of quality suitable for cutting at Mount Vesuvius in
Italy.
Like the ruby, Spinel can be made artificially, the process being to
heat a mixture of alumina and magnesia with boracic acid, and if the red
color is desired, a little chromium oxide.
The Spinel ruby seems to have been known to the ancients equally with
the corundum ruby, and the two were probably often confounded. The
natives of India call the Spinel the pomegranate ruby and believe to
this day that it possesses valuable medicinal properties.
Oliver Cummings Farrington.
[Illustration: WHITE-CROWNED SPARROW.
(Zonotrichia leucophrys).
Life-size.
FROM COL. CHI. ACAD. SCIENCES.]
THE WHITE-CROWNED SPARROW.
(_Zonotrichia leucophrys._)
With the snowflakes o’er the mountains
Hasten past the hawks from Northland,
Speed along the titmice, juncos,
White-crowned Sparrows, wrens, and creepers,
Tiny kinglets, sweet-voiced bluebirds,
All in eager search for havens
Where the touch of winter kills not.
—Frank Bolles, “Birds in October.”
Mr. Ernest E. Thompson calls the White-crowned Sparrow an aristocrat of
the sparrow family. One of the largest of the sparrows, its beautifully
marked plumage and its dignified mien, as it stands on some exposed
perch, immediately attracts the attention of an observer. Its range is
extensive, covering the whole of the United States during its
migrations, and in winter it passes further southward into the valley
regions of Mexico. In the selection of a nesting site a pure and cool
atmosphere seems a paramount consideration. The mountain regions of the
western United States and the country lying north of the great lakes and
eastward into Labrador seem to meet the requirements for the home
building of these sweet dispositioned birds. Then its music is sweetest.
During its migration, however, localities not favored with its home are
often regaled “with selections of its melodies as it rests in thickets
and hedgerows while slowly passing through our country on its northward
pilgrimage.” From some high bush or other favorable perch the male will
pour forth an almost unbroken song while its mate is setting. Often this
song does not cease with the going down of the sun, and it has been
heard as late as midnight. It is a “lively, agreeable song, fine and
clear, and is frequently heard from a score or more of birds at the same
time with a most pleasing effect.”
Its song, quite closely resembling that of its relative the
white-throated sparrow, with which it quite frequently consorts during
its migrations, yet the two songs are readily distinguishable. Mr.
Thompson compares the songs. He says: “Its usual song is like the latter
half of the white-throat’s familiar refrain, repeated a number of times
with a peculiar, sad cadence and a clear, soft whistle that is
characteristic of the group.” Dr. Coues, speaking of the two songs, says
that the song of the White-crowned Sparrow is “a less enterprising vocal
effort, of only five or six syllables, like pee, dee, de, de, de, the
two first long drawn, rising, the rest hurried and lowering.”
Transcribed into words, there are almost as many renderings of the
White-crowned’s song as there are observers. Mr. Burroughs says that the
song “begins with the words fe-u, fe-u, fe-u, and runs off into trills
and quavers like the song sparrow’s, only much more touching.” To Mr.
Langille “the song is quite peculiar, whee-who-who-zee-zee-zee, the
first three notes in a clear whistle and the last three in a sort of
jew’s-harp tone, the whole being decidedly pleasing, and not at all like
that of the white-throat.”
The food of the White-crowned sparrow consists of both insects and
seeds. To some extent they feed upon berries, and Audubon states that in
Labrador they also eat minute shellfish, “for which they frequently
search the margins of ponds or the seashore.” This bird is a scratcher.
It is also a hopper and hence scratches with both feet at once.
The nest of this Sparrow is usually constructed of grass or moss and is
placed either on the ground or in low bushes. Audubon describes a
beautiful nest of this species which he found in Labrador. This nest
“was placed in the moss, near the foot of a low fir, and was formed
externally of beautiful dry green moss, matted in bunches, like the
coarse hair of some quadruped; internally of very fine, dry grass,
arranged with great neatness, to the thickness of nearly half an inch,
with a full lining of delicate fibrous roots of a rich transparent
color.”
Of this beautiful Sparrow Mr. Burroughs has said: “Among the birds that
tarry briefly with us in the spring on their way to Canada and beyond,
there is none that I behold with so much pleasure as the White-crowned
Sparrow. I have an eye out for him all through April and the first week
in May. He is the rarest and most beautiful of the sparrow kind. He is
crowned as some hero or victor in the games. His sparrow color, of ashen
gray and brown, is very clear and bright, and his form graceful. His
whole expression, however, culminates in a regular manner in his crown.
The various tints of the bird are brought to a focus here and
intensified, the lighter ones becoming white and the deeper ones mainly
black. There is the suggestion of a crest also, from a habit this bird
has of slightly elevating this part of its plumage, as if to make more
conspicuous its pretty markings.”