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LAPIS LAZULI.
Lapis lazuli is a magnificent blue stone. Fine specimens are
used sometimes as gems, and their color is far more intense than
that of any other opaque blue stone. The sapphirus of the ancients
was lapis lazuli, not the specimen of corundum now bearing that
name. For centuries this stone was prized above all others, and for
the beauty of its color alone. This was the standard to which all
blues were compared. It is the only one resembling in purity of
color the blue of the spectrum. Eventually a process was discovered
for converting the dazzling tint into ultramarine. Nowadays cobalt
is the basis of that same hue. For long ultramarine came from Asia
hence its name "beyond the sea." Lapis lazuli may be considered
to contain natural ultramarine, and before the introduction of the
artificial, this pigment was very expensive. "Ultramarine ashes" is
the residuum left after the color has been extracted. It is used by
painters where a neutral tint is required, being of a purer and more
tender gray than that produced by a mixture of positive colors.
Lapis is not always deep blue: sometimes pale blue, greenish,
violet, reddish, pure green; sometimes flecked with yellow, shining,
metallic spots, due to iron pyrites. It is not a homogeneous stone,
mass is white cal-
but a mixture of several substances. The ground
cite. In this the various minerals are imbedded, in varying proportions.
Many of these are hornblende, but the remaining grains are
of the true lapis substance, and impart to the mineral its color and
other characteristics. If these are present in large quantities, the
color of the stone is deep and full; if not, their irregularity makes
it patchy. Its hardness is 5.5 ; specific gravity 2.5.
Lapis, in short, is a limestone, more or less impregnated with
pigment and probably formed by the action of granite on limestone,
through terrestrial fire. It is what is known as a "contact product."
The richest deposits are in Asia, but it is also found in Chili and
the neighborhood of Rome and Naples. Mines existed in Central
Asia as far back as Marco Polo. It is not as valuable as it once was.
The price depends on the purity and depth of color. It is used for
various articles, vases, bowls, candle-sticks, and also for decorating
interiors. The winter palace at St. Petersburg is thus decorated, and
San Martino, Naples. Imitations in glass, also colored agate and
azurite are all chemically different.
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