HORNBLENDE.--A mineral species, placed by Dana in the augite section
of the anhydrous silicates. In common use the name is limited, as it
was formerly applied only to the dark crystalline minerals which are
met with in long, slender prisms, either scattered in quartz, granite,
etc., or generally disseminated throughout their mass. The color of
the mineral is usually black or dark green, owing to the presence of
much iron. It appears to have been produced under conditions of fusion
and cooling which cannot be imitated in the laboratory, the crystals
obtained artificially being of augite type.
MALACHITE.--One of the native carbonates of copper. It is sometimes
crystallized, but more often occurs in concretionary masses of various
shades of green, which are generally banded or arranged in such a
manner that the mineral, which takes a fine polish, is much prized as
an ornamental stone. Great quantities of it are found in the Siberian
mines, and many beautiful objects are manufactured from it.
QUARTZ.--The most abundant of all minerals, existing as a constituent
of many rocks, composing of itself the rock known as quartzite or
quartz rock and some of the sandstones and pure sand, forming the
chief portion of most mineral veins. In composition it is silica, and
when uncontaminated with any foreign intermixture it appears in clear,
transparent crystals like glass or ice. Pure quartz is largely employed
in the manufacture of glass and is commonly obtained for this purpose
in the form of sand. Quartz veins with few exceptions form the gangues
in which gold is found.
TOURMALINE.--A name applied to a group of double silicates, composed
of many other minerals. The color of tourmalines varies with their
composition. The red, called rubellite, are manganese tourmaline
containing lithium and manganese, with little or no iron; the
violet, blue and green contain iron, and the black are either iron
or magnesium-iron tourmalines. Sometimes the crystals are red at
one extremity and green at the other, or green internally and red
externally, or _vice versa_. Pink crystals are found in the island of
Elba. Tourmalines are not often used in jewelry, although they form
beautiful gems and bear a high price. A magnificent group of pink
tourmalines, nearly a foot square, was given by the king of Burmah to
Col. Sykes, while commissioner to his court. The tourmaline appears to
have been brought to Europe from Ceylon by the Dutch about the end of
the seventeenth century, and was exhibited as a curiosity on account of
its pyro-electric properties.
AGATE.--Of the quartz family, and is one of the modifications in
which silica presents itself nearly in a state of purity. Agates are
distinguished from the other varieties by the veins of different shades
of color which traverse the stone in parallel concentric layers,
often so thin as to number fifty or more to an inch. Externally the
agates are rough and exhibit no appearance of their beautiful, veined
structure, which is exposed on breaking them, and still more perfectly
after polishing. Though the varieties of agate are mostly very common
minerals in this country as well as in the old world, those localities
only are of interest which have long been famous for their production
and which still furnish all the agates required by commerce.
AMETHYST.--So named because it was supposed by the ancient Persians
that cups made of it would prevent the liquor they contained from
intoxicating. The stone consists of crystallized quartz of a purple or
blue violet color, probably derived from a compound of iron and soda.
The color is not always diffused through it, and is less brilliant by
candlelight.
SERPENTINE.--Serpentine differs in composition from the other marbles.
It is a soft mineral of different shades of green, of waxy luster, and
susceptible of a high polish. It is better adapted to ornamental
work within doors than to be exposed to the action of the weather.
SULPHUR.--An elementary substance belonging to the class of
metalloids. It has been known from the earliest times as the product
of volcanoes, and as a natural mineral deposit in clay and marl
formations. It also exists in primitive rocks, as granite and mica.